Electricity MCQ Class 10 Quiz. Revise Class 10 Electricity topics with these MCQs. Questions on current, potential difference, Ohm’s law, resistance, and circuits.
Electricity MCQ Class 10 Quiz Topics:
Introduction to Electric Current & Circuits: MCQ 1–15
Electric Potential and Potential Difference: MCQ 16–30
Question 1: What is the direction of electric current in an electric circuit?
A. From the negative terminal of the cell to the positive terminal
B. From the positive terminal of the cell to the negative terminal
C. In the same direction as the flow of electrons
D. Varies depending on the type of cell
B. From the positive terminal of the cell to the negative terminal. By convention, the direction of electric current (conventional current) is defined as the direction positive charges would flow, which is from the positive terminal to the negative terminal in an external circuit. This is opposite to the actual flow of electrons.
Question 2: Which of the following is the SI unit of electric charge?
A. Ampere
B. Coulomb
C. Volt
D. Ohm
B. Coulomb. The coulomb (C) is the standard unit of electric charge in the International System of Units (SI).
Question 3: What is the unit of electric current?
A. Coulomb
B. Volt
C. Ampere
D. Ohm
C. Ampere. The ampere (A) is the SI base unit used to measure electric current.
Question 4: How many electrons approximately make up one coulomb of charge?
A. 6 × 10¹⁸
B. 1.6 × 10⁻¹⁹
C. 1
D. 6 × 10⁻¹⁸
A. 6 × 10¹⁸. The elementary charge (charge of one electron) is approximately 1.602 × 10⁻¹⁹ C. Therefore, one coulomb contains about 1 ⁄ (1.602 × 10⁻¹⁹) ≈ 6.24 × 10¹⁸ electrons, which is commonly approximated as 6 × 10¹⁸.
Question 5: Which instrument is used to measure electric current in a circuit?
A. Voltmeter
B. Ammeter
C. Galvanometer
D. Ohmmeter
B. Ammeter. An ammeter is designed to measure the rate of flow of electric charge, which is the electric current.
Question 6: How is an ammeter connected in a circuit to measure current?
A. In parallel
B. In series
C. Either in parallel or series
D. Neither in parallel nor series
B. In series. To measure the total current flowing through a part of a circuit, the ammeter must be placed in series, so all the charge flows through it.
Question 7: What does an electric circuit mean?
A. A continuous and closed path of an electric current
B. A discontinuous and open path of an electric current
C. A combination of cells and a bulb
D. A combination of cells, a bulb, and a switch
A. A continuous and closed path of an electric current. For a steady current to flow, there must be an unbroken, conducting loop connecting the terminals of the energy source.
Question 8: Which of the following is NOT a necessary component of a simple electric circuit?
A. Battery
B. Resistor
C. Switch
D. Voltmeter
D. Voltmeter. A basic functional circuit needs an energy source (like a battery), a conductive path (wires), and a load (like a resistor or bulb) to consume energy. A switch is for control. A voltmeter measures potential difference and is not required for the circuit to operate.
Question 9: What constitutes the flow of charges in circuits using metallic wires?
A. Protons
B. Electrons
C. Neutrons
D. Ions
B. Electrons. In solid metallic conductors, the charge carriers are the free valence electrons, which can move throughout the metal lattice.
Question 10: A current of 2 A flows through a conductor for 5 seconds. Calculate the amount of electric charge that flows through the conductor.
A. 0.4 C
B. 2.5 C
C. 7 C
D. 10 C
D. 10 C. Electric charge (Q) is calculated by multiplying the current (I) by the time (t) for which it flows: Q = I × t = 2 A × 5 s = 10 C.
Question 11: If 50 C of charge flows through a conductor in 10 seconds, what is the current flowing through the conductor?
A. 500 A
B. 60 A
C. 5 A
D. 0.2 A
C. 5 A. Electric current (I) is the rate of flow of charge (Q) over time (t): I = Q ⁄ t = 50 C ⁄ 10 s = 5 A.
Question 12: A current of 200 mA flows through a bulb. What is the current in amperes?
A. 2 A
B. 0.2 A
C. 0.02 A
D. 0.002 A
B. 0.2 A. The prefix ‘milli’ (m) represents 10⁻³. So, 200 mA = 200 × 10⁻³ A = 0.2 A.
Question 13: A current of 5 μA flows through a resistor. What is the current in amperes?
A. 5 × 10⁻⁶ A
B. 5 × 10⁻³ A
C. 5 × 10³ A
D. 5 × 10⁶ A
A. 5 × 10⁻⁶ A. The prefix ‘micro’ (μ) represents 10⁻⁶. So, 5 μA = 5 × 10⁻⁶ A.
Question 14: What is the role of a switch in an electric circuit?
A. To provide energy to the circuit
B. To measure the current in the circuit
C. To make or break the flow of current in the circuit
D. To resist the flow of current in the circuit
C. To make or break the flow of current in the circuit. A switch is used to conveniently open (break) or close (make) the conducting path of the circuit.
Question 15: What happens when the switch of a torch is turned off?
A. The current continues to flow, and the bulb glows.
B. The current stops flowing, but the bulb glows.
C. The current stops flowing, and the bulb does not glow.
D. The current continues to flow, but the bulb does not glow.
C. The current stops flowing, and the bulb does not glow. Turning the switch off creates a break (open circuit) in the path, interrupting the flow of current, which stops the bulb from glowing.
Question 16: What makes an electric charge flow through a conductor?
A. Gravity
B. Pressure difference
C. Potential difference
D. Temperature difference
C. Potential difference. A difference in electric potential (voltage) between two points in a conductor creates an electric field that exerts a force on charge carriers, causing them to move (flow).
Question 17: What is the SI unit of electric potential difference?
A. Ampere
B. Coulomb
C. Volt
D. Ohm
C. Volt. The volt (V) is the SI derived unit for electric potential difference (or voltage).
Question 18: Which device helps to maintain a potential difference across a conductor?
A. Ammeter
B. Voltmeter
C. Battery
D. Resistor
C. Battery. A battery (or cell, or power supply) converts chemical energy into electrical energy to maintain a potential difference between its terminals, driving current through an external circuit.
Question 19: What is meant by saying that the potential difference between two points is 1 V?
A. 1 joule of work is done to move a charge of 1 coulomb from one point to another.
B. 1 coulomb of charge is moved from one point to another in 1 second.
C. 1 ampere of current flows between the two points when 1 ohm of resistance is connecte
D. D. 1 joule of energy is given to each electron moving between the two points.
A. 1 joule of work is done to move a charge of 1 coulomb from one point to another. This is the definition of the volt: 1 V = 1 Joule⁄Coulomb.
Question 20: How much energy is given to each coulomb of charge passing through a 10 V battery?
A. 1 joule
B. 10 joules
C. 100 joules
D. 0.1 joules
B. 10 joules. Potential difference (V) is defined as energy (E) per unit charge (Q), so E = V × Q. For V=10 V and Q=1 C, the energy is E = 10 V × 1 C = 10 J.
Question 21: How much work is done in moving a charge of 5 C across two points having a potential difference of 10 V?
A. 2 J
B. 5 J
C. 15 J
D. 50 J
D. 50 J. Work done (W) in moving a charge (Q) across a potential difference (V) is given by W = Q × V = 5 C × 10 V = 50 J.
Question 22: If 100 J of work is done to move a charge of 20 C across two points, what is the potential difference between the two points?
A. 5 V
B. 20 V
C. 80 V
D. 120 V
A. 5 V. Potential difference (V) is work done (W) per unit charge (Q): V = W ⁄ Q = 100 J ⁄ 20 C = 5 V.
Question 23: What is the relationship between the potential difference across a conductor and the current flowing through it, provided its temperature remains constant?
A. Directly proportional
B. Inversely proportional
C. No relationship
D. Exponentially proportional
A. Directly proportional. This is a statement of Ohm’s Law (V = IR), which applies to many conductors (ohmic conductors) under constant temperature. Voltage is directly proportional to current.
Question 24: Which instrument is used to measure the potential difference across a conductor?
A. Ammeter
B. Voltmeter
C. Galvanometer
D. Ohmmeter
B. Voltmeter. A voltmeter is designed to measure the electric potential difference (voltage) between two points in a circuit.
Question 25: How is a voltmeter connected in a circuit to measure the potential difference across a component?
A. In series
B. In parallel
C. Either in series or parallel
D. Neither in series nor parallel
B. In parallel. A voltmeter is connected in parallel (across) the component whose potential difference is being measured.
Question 26: What is the potential difference between the terminals of a battery if it does 36 J of work in moving a charge of 4 C around a circuit?
A. 9 V
B. 144 V
C. 40 V
D. 32 V
A. 9 V. The potential difference (V) provided by the battery is the work done (W) per unit charge (Q): V = W ⁄ Q = 36 J ⁄ 4 C = 9 V.
Question 27: If a battery provides a potential difference of 12 V, how much work is done in moving 2 C of charge through a circuit?
A. 6 J
B. 10 J
C. 14 J
D. 24 J
D. 24 J. Work done (W) is the product of charge (Q) and potential difference (V): W = Q × V = 2 C × 12 V = 24 J.
Question 28: What is the function of a battery in an electric circuit?
A. To measure the current
B. To break the circuit
C. To provide a potential difference
D. To oppose the flow of current
C. To provide a potential difference. The battery acts as the energy source, establishing the potential difference (voltage) that drives the current through the circuit.
Question 29: What happens to the potential difference across a conductor if the current through it increases?
A. It increases.
B. It decreases.
C. It remains the same.
D. It depends on the resistance of the conductor.
A. It increases. Assuming the conductor obeys Ohm’s Law (V=IR) and its resistance (R) is constant, the potential difference (V) is directly proportional to the current (I). Therefore, if the current increases, the potential difference across the conductor also increases.
Question 30: Why does a bulb glow when connected to a battery?
A. Because the battery provides a path for the current to flow
B. Because the battery creates a potential difference across the bulb
C. Because the battery heats up the bulb filament
D. Because the battery provides electrons to the bulb
B. Because the battery creates a potential difference across the bulb. This potential difference causes current to flow through the filament. The filament’s resistance converts electrical energy into heat and light (heating effect).
Question 31: What is a circuit diagram?
A. A photograph of an electric circuit
B. A drawing of an electric circuit using actual pictures of the components
C. A simplified drawing of an electric circuit using standard symbols for components
D. A drawing showing the flow of electrons in an electric circuit
C. A simplified drawing of an electric circuit using standard symbols for components. Circuit diagrams provide a schematic representation using universally recognized symbols for clarity and ease of understanding.
Question 32: Why are circuit diagrams used?
A. To make the representation of electrical circuits complex and detailed
B. To represent electrical circuits in a simpler and more understandable way
C. To show the actual physical size of electrical components
D. To show the flow of electrons in a circuit
B. To represent electrical circuits in a simpler and more understandable way. Standard symbols abstract away physical details, focusing on the connections and function of the circuit.
Question 33: What does the symbol ‘—[ ]—’ represent in a circuit diagram?
A. An open switch
B. A closed switch
C. A cell
D. A battery
B. A closed switch. Based on the symbols provided in this set of questions (specifically comparing with Q39), this symbol represents a closed switch, indicating a complete path.
Question 34: What does the symbol ‘—•—’ represent in a circuit diagram?
A. A resistor
B. An ammeter
C. A voltmeter
D. A bulb
A. A resistor. Although a zigzag line (‘—/\/\/\—’) is the standard symbol, in the context of these questions, ‘—•—’ is indicated as representing a resistor.
Question 35: What does the symbol ‘—A—’ represent in a circuit diagram?
A. An ammeter
B. A voltmeter
C. A cell
D. A battery
A. An ammeter. The letter ‘A’, often enclosed in a circle ‘—(A)—’, is the standard symbol for an ammeter.
Question 36: What does the symbol ‘—V—’ represent in a circuit diagram?
A. A voltmeter
B. An ammeter
C. A cell
D. A battery
A. A voltmeter. The letter ‘V’, often enclosed in a circle ‘—(V)—’, is the standard symbol for a voltmeter.
Question 37: How is a battery represented in a circuit diagram?
A. ‘—|—’
B. ‘—||—’
C. ‘—[ ]—’
D. ‘—•—’
B. ‘—||—’. This symbol strictly represents a single electric cell. A battery (multiple cells) is often shown as ‘—|i|i|—’, but this single cell symbol is frequently used to represent a general DC voltage source or battery in simple diagrams.
Question 38: What does a long line and a short line together represent in a circuit diagram of a cell?
A. Positive and negative terminals of the cell, respectively
B. Negative and positive terminals of the cell, respectively
C. Both lines represent the positive terminals of the cell
D. Both lines represent the negative terminals of the cell
A. Positive and negative terminals of the cell, respectively. In the standard symbol for a cell (‘—||—’), the longer line denotes the positive (+) terminal, and the shorter line denotes the negative (-) terminal.
Question 39: How is an open switch represented in a circuit diagram?
A. ‘—[ ]—’
B. ‘—/ \’
C. ‘—•—’
D. ‘—||—’
B. ‘—/ \’. This symbol shows a break in the line, representing an open switch that interrupts the circuit path.
Question 40: Why are symbols used to represent components in circuit diagrams?
A. To make the diagrams more visually appealing
B. To make the diagrams universally understandable
C. To complicate the understanding of electrical circuits
D. To show the actual physical appearance of components
B. To make the diagrams universally understandable. Using standardized symbols ensures that engineers and technicians worldwide can interpret circuit diagrams consistently.
Question 41: What is the relationship between the current flowing through a conductor and the potential difference across its ends?
A. Directly proportional
B. Inversely proportional
C. No relationship
D. Exponentially proportional
A. Directly proportional. According to Ohm’s Law, for an ohmic conductor at constant temperature, the current is directly proportional to the applied potential difference (I ∝ V).
Question 42: What is the resistance of a conductor?
A. The opposition offered to the flow of current by the conductor
B. The potential difference across the conductor
C. The current flowing through the conductor
D. The power consumed by the conductor
A. The opposition offered to the flow of current by the conductor. Resistance quantifies how much a material impedes the flow of electric charge.
Question 43: What is the SI unit of resistance?
A. Ampere
B. Volt
C. Ohm
D. Coulomb
C. Ohm. The ohm (Ω) is the SI unit of electrical resistance, defined as volts per ampere.
Question 44: What is Ohm’s law?
A. The current flowing through a conductor is directly proportional to the square of the potential difference across its ends, provided the temperature remains constant.
B. The current flowing through a conductor is inversely proportional to the potential difference across its ends, provided the temperature remains constant.
C. The current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant.
D. The resistance of a conductor is directly proportional to the current flowing through it, provided the potential difference remains constant.
C. The current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant. Mathematically stated as V=IR or I=V⁄R.
Question 45: If the potential difference across a conductor is doubled, what happens to the current flowing through it, assuming the temperature remains constant?
A. It halves
B. It doubles
C. It remains the same
D. It quadruples
B. It doubles. From Ohm’s Law (I = V⁄R), if V is doubled and R is constant, I must also double.
Question 46: If the resistance of a conductor is doubled, what happens to the current flowing through it, assuming the potential difference remains constant?
A. It halves
B. It doubles
C. It remains the same
D. It quadruples
A. It halves. From Ohm’s Law (I = V⁄R), if R is doubled and V is constant, I must become half of its original value.
Question 47: A potential difference of 10 V is applied across a conductor with a resistance of 5 Ω. What is the current flowing through the conductor?
A. 0.5 A
B. 2 A
C. 15 A
D. 50 A
B. 2 A. Using Ohm’s Law, I = V⁄R = 10 V ⁄ 5 Ω = 2 A.
Question 48: A current of 2 A flows through a conductor when a potential difference of 20 V is applied across it. What is the resistance of the conductor?
A. 0.1 Ω
B. 10 Ω
C. 22 Ω
D. 40 Ω
B. 10 Ω. Using Ohm’s Law, R = V⁄I = 20 V ⁄ 2 A = 10 Ω.
Question 49: What is a rheostat?
A. A device used to measure current
B. A device used to measure potential difference
C. A device used to provide a constant resistance
D. A device used to provide a variable resistance
D. A device used to provide a variable resistance. A rheostat is a type of variable resistor, typically used to control the current in a circuit.
Question 50: How is a rheostat used in a circuit?
A. To change the current in the circuit
B. To change the potential difference across a component
C. To measure the resistance of a component
D. To break the circuit
A. To change the current in the circuit. By adjusting the rheostat’s resistance, the total resistance of the circuit changes, which in turn changes the current according to Ohm’s Law (assuming constant voltage).
Question 51: What happens to the current in a circuit when the resistance is increased?
A. It increases.
B. It decreases.
C. It remains the same.
D. It depends on the potential difference.
B. It decreases. According to Ohm’s Law (I=V⁄R), if the total resistance (R) increases while the voltage (V) remains constant, the current (I) must decrease.
Question 52: What happens to the brightness of a bulb when the current through it decreases?
A. It increases.
B. It decreases.
C. It remains the same.
D. It depends on the voltage across the bulb.
B. It decreases. The brightness is related to the power dissipated (P=I²R). If the current (I) decreases, the power dissipated as heat and light decreases, making the bulb dimmer.
Question 53: Why does the current increase when more cells are added to a circuit in series?
A. Because the total resistance of the circuit increases
B. Because the total potential difference across the circuit increases
C. Because the total current in the circuit decreases
D. Because the total resistance of the circuit decreases
B. Because the total potential difference across the circuit increases. Connecting cells in series adds their voltages. With increased total voltage (V) and assuming resistance (R) is constant, the current (I=V⁄R) increases.
Question 54: What is the equivalent resistance of two resistors of 2 Ω and 3 Ω connected in series?
A. 1 Ω
B. 1.2 Ω
C. 5 Ω
D. 6 Ω
C. 5 Ω. For resistors in series, the equivalent resistance (Rₑ<0xE1><0xB5><0xA1>) is the sum of individual resistances: Rₑ<0xE1><0xB5><0xA1> = R₁ + R₂ = 2 Ω + 3 Ω = 5 Ω.
Question 55: What is the equivalent resistance of two resistors of 4 Ω and 4 Ω connected in parallel?
A. 8 Ω
B. 4 Ω
C. 2 Ω
D. 1 Ω
C. 2 Ω. For resistors in parallel, 1⁄Rₑ<0xE1><0xB5><0xA1> = 1⁄R₁ + 1⁄R₂. So, 1⁄Rₑ<0xE1><0xB5><0xA1> = 1⁄(4 Ω) + 1⁄(4 Ω) = 2⁄(4 Ω) = 1⁄(2 Ω). Therefore, Rₑ<0xE1><0xB5><0xA1> = 2 Ω.
Question 56: What factors affect the resistance of a conductor?
A. Length, cross-sectional area, and temperature
B. Length, cross-sectional area, and material
C. Length, material, and current
D. Material, current, and potential difference
B. Length, cross-sectional area, and material. The resistance (R) is given by R = ρL⁄A, where L is length, A is cross-sectional area, and ρ is the resistivity (a property of the material). Temperature also affects resistivity (ρ) and thus resistance.
Question 57: How does the resistance of a wire vary with its length?
A. Directly proportional
B. Inversely proportional
C. No relationship
D. Exponentially proportional
A. Directly proportional. Resistance is directly proportional to length (R ∝ L), meaning a longer wire has more resistance, all else being equal.
Question 58: How does the resistance of a wire vary with its cross-sectional area?
A. Directly proportional
B. Inversely proportional
C. No relationship
D. Exponentially proportional
B. Inversely proportional. Resistance is inversely proportional to the cross-sectional area (R ∝ 1⁄A), meaning a thicker wire (larger area) has less resistance, all else being equal.
Question 59: If the length of a wire is doubled, what happens to its resistance?
A. It halves
B. It doubles
C. It remains the same
D. It quadruples
B. It doubles. Since R ∝ L, doubling L doubles R.
Question 60: If the cross-sectional area of a wire is doubled, what happens to its resistance?
A. It halves
B. It doubles
C. It remains the same
D. It quadruples
A. It halves. Since R ∝ 1⁄A, doubling A makes R half its original value.
Question 61: What is resistivity?
A. The resistance of a conductor of unit length and unit cross-sectional area
B. The conductance of a conductor of unit length and unit cross-sectional area
C. The potential difference across a conductor of unit length and unit cross-sectional area
D. The current flowing through a conductor of unit length and unit cross-sectional area
A. The resistance of a conductor of unit length and unit cross-sectional area. Resistivity (ρ) is an intrinsic material property defined by R = ρL⁄A. It represents the resistance of a standard cube (e.g., 1m x 1m x 1m) of the material.
Question 62: What is the SI unit of resistivity?
A. Ohm
B. Ohm-meter
C. Ohm per meter
D. Meter per ohm
B. Ohm-meter. From ρ = RA⁄L, the units are Ω⋅m² ⁄ m = Ω⋅m.
Question 63: Which of the following materials has the highest resistivity?
A. Silver
B. Copper
C. Aluminum
D. Nichrome
D. Nichrome. Silver, copper, and aluminum are excellent conductors with very low resistivity. Nichrome (an alloy of nickel and chromium) has significantly higher resistivity and is used in heating elements.
Question 64: Why are copper and aluminum wires usually employed for electricity transmission?
A. Because they have high resistivity
B. Because they are good insulators
C. Because they have low resistivity
D. Because they are easily available
C. Because they have low resistivity. Low resistivity minimizes energy loss (P=I²R) due to heat during the transmission of electrical power over long distances.
Question 65: What is the difference between a good conductor and a poor conductor of electricity?
A. A good conductor has low resistivity, while a poor conductor has high resistivity.
B. A good conductor has high resistivity, while a poor conductor has low resistivity.
C. A good conductor allows current to flow through it easily, while a poor conductor does not allow current to flow through it at all.
D. A good conductor has a high melting point, while a poor conductor has a low melting point.
A. A good conductor has low resistivity, while a poor conductor has high resistivity. Low resistivity facilitates easy current flow (conductor), while high resistivity impedes it (poor conductor or insulator).
Question 66: What is the equivalent resistance of two resistors connected in series?
A. The sum of their individual resistances
B. The product of their individual resistances
C. The difference between their individual resistances
D. The ratio of their individual resistances
A. The sum of their individual resistances. Rₑ<0xE1><0xB5><0xA1>(series) = R₁ + R₂ + … + R<0xE2><0x82><0x99>.
Question 67: What is the equivalent resistance of two resistors connected in parallel?
A. The sum of their individual resistances
B. The product of their individual resistances divided by their sum
C. The difference between their individual resistances
D. The ratio of their individual resistances
B. The product of their individual resistances divided by their sum. The general formula is 1⁄Rₑ<0xE1><0xB5><0xA1>(parallel) = 1⁄R₁ + 1⁄R₂ + …. For two resistors, this simplifies to Rₑ<0xE1><0xB5><0xA1> = (R₁R₂) ⁄ (R₁ + R₂).
Question 68: What is the equivalent resistance of three resistors of 2 Ω, 4 Ω, and 6 Ω connected in series?
Question 70: In a series circuit, which of the following remains the same across all resistors?
A. Current
B. Potential difference
C. Both current and potential difference
D. Neither current nor potential difference
A. Current. There is only one path for charge flow in a simple series circuit, so the current is the same through all components.
Question 71: In a parallel circuit, which of the Ffollowing remains the same across all resistors?
A. Current
B. Potential difference
C. Both current and potential difference
D. Neither current nor potential difference
B. Potential difference. Components connected in parallel share the same two connection points, so the voltage across each component is identical.
Question 72: Why is the series arrangement not used for domestic circuits?
A. Because the current remains the same in all appliances, and they may not operate properly.
B. Because the potential difference remains the same across all appliances, and they may not operate properly.
C. Because if one appliance fails, all other appliances in the circuit will also stop working.
D. Because it is difficult to connect appliances in series.
C. Because if one appliance fails, all other appliances in the circuit will also stop working. A break anywhere in a series circuit interrupts the entire path, causing all devices to cease functioning. Also, voltage divides across series components, which isn’t suitable for appliances designed for a standard voltage.
Question 73: What happens to the total resistance of a circuit when resistors are added in series?
A. It increases.
B. It decreases.
C. It remains the same.
D. It depends on the value of the resistors.
A. It increases. The total resistance in series is the sum of individual resistances, so adding more resistors always increases the total.
Question 74: What happens to the total resistance of a circuit when resistors are added in parallel?
A. It increases.
B. It decreases.
C. It remains the same.
D. It depends on the value of the resistors.
B. It decreases. Adding parallel paths provides more ways for current to flow, reducing the overall opposition. The equivalent resistance is always less than the smallest individual resistance in the parallel group.
Question 75: Two resistors of 4 Ω and 6 Ω are connected in parallel. What is their equivalent resistance?
Question 79: Why do we use parallel circuits in homes?
A. Because the current is the same in all appliances
B. Because the potential difference is the same across all appliances
C. Because if one appliance fails, the others continue to work
D. Because it is easier to connect appliances in parallel
C. Because if one appliance fails, the others continue to work. This provides reliability. Additionally, parallel wiring ensures each appliance receives the full supply voltage (as stated in B), which is necessary for proper operation.
Question 80: What is the advantage of connecting electrical devices in parallel with the battery instead of connecting them in series?
A. The current through each appliance is greater in the parallel circuit.
B. The potential difference across each appliance is greater in the parallel circuit.
C. The power consumed by each appliance is greater in the parallel circuit.
D. If one appliance fails, the others continue to work in the parallel circuit.
D. If one appliance fails, the others continue to work in the parallel circuit. This independent operation is a key benefit over series connections for household wiring.
Question 81: What happens when an electric current flows through a conductor?
A. It produces light.
B. It produces heat.
C. It produces magnetic effects.
D. All of the above.
D. All of the above. Current flow invariably produces heat (P=I²R) and a magnetic field around the conductor. Light is produced if the heating is intense enough (incandescence) or via other mechanisms (e.g., LEDs).
Question 82: What is the heating effect of electric current?
A. The conversion of electrical energy into heat energy
B. The conversion of heat energy into electrical energy
C. The production of light when current flows through a conductor
D. The production of magnetic fields when current flows through a conductor
A. The conversion of electrical energy into heat energy. As charges move through a resistive material, they collide with atoms, transferring energy and increasing the material’s internal energy, which manifests as heat. This is also called Joule heating.
Question 83: What is Joule’s law of heating?
A. The heat produced in a resistor is directly proportional to the square of the current, the resistance, and the time for which the current flows.
B. The heat produced in a resistor is inversely proportional to the square of the current, the resistance, and the time for which the current flows.
C. The heat produced in a resistor is directly proportional to the current, the resistance, and inversely proportional to the time for which the current flows.
D. The heat produced in a resistor is inversely proportional to the current, the resistance, and directly proportional to the time for which the current flows.
A. The heat produced in a resistor is directly proportional to the square of the current, the resistance, and the time for which the current flows. The law states that the heat (H) generated is H = I²Rt.
Question 84: What is the formula for calculating the heat produced in a resistor?
A. H = I²Rt
B. H = IR²t
C. H = I²R⁄t
D. H = IR⁄t²
A. H = I²Rt. This is the mathematical expression of Joule’s law of heating, where H is heat energy, I is current, R is resistance, and t is time.
Question 85: What happens to the heat produced in a resistor if the current flowing through it is doubled?
A. It doubles.
B. It quadruples.
C. It halves.
D. It remains the same.
B. It quadruples. Since H ∝ I², if I becomes 2I, then H becomes proportional to (2I)² = 4I². The heat produced increases by a factor of 4.
Question 86: What happens to the heat produced in a resistor if the resistance is doubled?
A. It doubles.
B. It quadruples.
C. It halves.
D. It remains the same.
A. It doubles. Since H ∝ R (assuming I and t are constant), if R becomes 2R, then H becomes 2H. The heat produced doubles.
Question 87: Which of the following is NOT an application of the heating effect of electric current?
A. Electric heater
B. Electric bulb
C. Electric motor
D. Fuse
C. Electric motor. Electric motors operate based on the magnetic effect of electric current (force on a current-carrying wire in a magnetic field), not the heating effect. Heaters, incandescent bulbs, and fuses directly utilize I²R heating.
Question 88: How does a fuse work?
A. It breaks the circuit when excessive current flows through it, due to the melting of a wire with a low melting point.
B. It increases the current in the circuit when excessive current flows through it.
C. It decreases the resistance of the circuit when excessive current flows through it.
D. It prevents any current from flowing through the circuit.
A. It breaks the circuit when excessive current flows through it, due to the melting of a wire with a low melting point. The fuse wire heats up (H=I²Rt) and melts when the current exceeds its rating, creating an open circuit and protecting downstream components.
Question 89: Why is the filament of an electric bulb made of tungsten?
A. Because it has a low melting point
B. Because it has a high melting point
C. Because it is a good conductor of electricity
D. Because it is easily available
B. Because it has a high melting point. Tungsten’s extremely high melting point (approx. 3422 °C) allows the filament to reach the high temperatures needed for incandescence (glowing white-hot) without melting.
Question 90: Why are electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
A. Because alloys have a lower melting point than pure metals
B. Because alloys have a higher melting point than pure metals
C. Because alloys are better conductors of electricity than pure metals
D. Because alloys are cheaper than pure metals
B. Because alloys have a higher melting point than pure metals. Alloys like nichrome are chosen for heating elements because they possess both high resistivity (to generate heat efficiently, P=I²R) and a high melting point to withstand the operating temperatures.
Question 91: What is electric power?
A. The rate at which electric energy is consumed or dissipated
B. The amount of electric energy consumed
C. The potential difference across a conductor
D. The current flowing through a conductor
A. The rate at which electric energy is consumed or dissipated. Power (P) is defined as energy (E) transferred or converted per unit time (t), i.e., P = E⁄t.
Question 92: What is the SI unit of power?
A. Joule
B. Watt
C. Volt
D. Ampere
B. Watt. The watt (W) is the SI unit of power, equivalent to one joule per second (1 W = 1 J⁄s).
Question 93: What is the formula for calculating power in terms of potential difference and current?
A. P = VI
B. P = V⁄I
C. P = I⁄V
D. P = V²I
A. P = VI. Electric power (P) is the product of the potential difference (V) and the current (I).
Question 94: What is the formula for calculating power in terms of current and resistance?
A. P = I²R
B. P = I⁄R²
C. P = R⁄I²
D. P = IR
A. P = I²R. Derived from P=VI and Ohm’s law (V=IR).
Question 95: What is the formula for calculating power in terms of potential difference and resistance?
A. P = V²⁄R
B. P = V⁄R²
C. P = R⁄V²
D. P = VR
A. P = V²⁄R. Derived from P=VI and Ohm’s law (I=V⁄R).
Question 96: What is the power consumed by an electrical appliance with a resistance of 10 Ω when connected to a 220 V line?
A. 22 W
B. 2200 W
C. 4840 W
D. 2.2 W
C. 4840 W. Using P = V²⁄R = (220 V)² ⁄ (10 Ω) = 48400 ⁄ 10 W = 4840 W.
Question 97: What is the current drawn by a 100 W bulb connected to a 220 V line?
A. 2.2 A
B. 0.45 A
C. 22000 A
D. 0.0045 A
B. 0.45 A. Using P = VI, the current I = P⁄V = 100 W ⁄ 220 V ≈ 0.4545 A.
Question 98: What is a kilowatt-hour (kWh)?
A. A unit of power
B. A unit of energy
C. A unit of time
D. A unit of current
B. A unit of energy. It represents the energy consumed when 1 kilowatt of power is used for 1 hour (Energy = Power × Time).
Question 99: How many joules are there in 1 kWh?
A. 3.6 × 10⁶ J
B. 3.6 × 10⁻⁶ J
C. 1000 J
D. 100 J
A. 3.6 × 10⁶ J. 1 kWh = (1000 W) × (3600 s) = 3,600,000 W⋅s = 3,600,000 J = 3.6 × 10⁶ J.
Question 100: What is the commercial unit of electrical energy?
A. Joule
B. Watt
C. Kilowatt-hour
D. Ampere-hour
C. Kilowatt-hour. Utility companies measure and bill for electrical energy consumption in kilowatt-hours (kWh), often called “units”.
