Q1. What is the SI unit of electric charge?
a) Ampere (A)
b) Coulomb (C)
c) Ohm (Ω)
d) Volt (V)
Answer: b) Coulomb (C)
Explanation: The SI unit of electric charge is the Coulomb (C), which represents the amount of charge contained in nearly 6 × 10^18 electrons.
Q2. According to Ohm’s Law, the current through a conductor between two points is directly proportional to the voltage across the two points. This statement is:
a) True, only if the temperature remains constant
b) False, the current is inversely proportional to the voltage
c) True, regardless of the temperature
d) False, the current is unrelated to the voltage
Answer: a) True, only if the temperature remains constant
Explanation: Ohm’s Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant.
Q3. The resistance of a wire is determined by which of the following factors?
a) Only the material of the wire
b) The length and diameter of the wire
c) The length, diameter, and material of the wire
d) Only the length of the wire
Answer: c) The length, diameter, and material of the wire
Explanation: The resistance of a conductor depends on its length, area of cross-section (which is related to the diameter), and the material of the conductor.
Q4. Which of the following is a correct expression of power in an electric circuit?
a) P = I/R
b) P = V/I
c) P = VI
d) P = IR^2
Answer: c) P = VI
Explanation: Power in an electric circuit is given by the product of the voltage (V) and the current (I), thus P = VI.
Q5. How is an ammeter connected in an electric circuit?
a) In series
b) In parallel
c) Directly across the voltage source
d) Not connected to the circuit
Answer: a) In series
Explanation: An ammeter, which measures electric current, is always connected in series with the circuit through which the current is to be measured.
Q6. What will be the effect on the current flowing through a circuit if the resistance is doubled and the voltage remains constant?
a) The current will double
b) The current will remain the same
c) The current will be halved
d) The current will quadruple
Answer: c) The current will be halved
Explanation: According to Ohm’s law, the current is inversely proportional to the resistance for a given voltage. Therefore, if the resistance is doubled, the current will be halved.
Q7. What happens to the resistance of a conductor if its length is doubled and its cross-sectional area is also doubled?
a) The resistance remains unchanged
b) The resistance is halved
c) The resistance is doubled
d) The resistance quadruples
Answer: a) The resistance remains unchanged
Explanation: The resistance of a conductor is directly proportional to its length and inversely proportional to its area of cross-section. Doubling both length and area keeps the resistance unchanged.
Q8. Which of the following devices is used to measure electric potential difference between two points?
a) Ammeter
b) Voltmeter
c) Ohmmeter
d) Galvanometer
Answer: b) Voltmeter
Explanation: A voltmeter is used to measure the electric potential difference between two points in an electric circuit and is connected in parallel to the component across which the measurement is made.
Q9. The heating effect of electric current is utilized in which of the following appliances?
a) Electric fan
b) Electric heater
c) Electric motor
d) All of the above
Answer: b) Electric heater
Explanation: The heating effect of electric current is utilized in appliances like electric heaters, where the electric energy is converted into heat energy.
Q10. If the potential difference across a circuit is doubled while the resistance remains constant, the power consumed will:
a) Remain the same
b) Double
c) Quadruple
d) Halve
Answer: c) Quadruple
Explanation: Power is given by the formula
=
2
P=
R
V
2
. If the potential difference is doubled and resistance remains constant, the power consumed quadruples.
Q11. An electric bulb of 100 W is used for 10 hours. The energy consumed is measured in:
a) Watts
b) Joules
c) Kilowatt-hours
d) Ampere-hours
Answer: c) Kilowatt-hours
Explanation: The energy consumed by electrical appliances is typically measured in kilowatt-hours. A 100 W bulb used for 10 hours consumes 1 kWh of energy.
Q12. The principle of the electric fuse is based on the:
a) Magnetic effect of electric current
b) Chemical effect of electric current
c) Heating effect of electric current
d) Mechanical effect of electric current
Answer: c) Heating effect of electric current
Explanation: The electric fuse operates based on the heating effect of electric current. It melts and breaks the circuit when the current exceeds a safe limit, preventing damage to the circuit and appliances.
Q13. What unit is used to measure the rate of flow of electric charge?
a) Joule
b) Coulomb
c) Ampere
d) Watt
Answer: c) Ampere
Explanation: The ampere is the unit used to measure the rate of flow of electric charge, representing the flow of one coulomb of charge per second.
Q14. Which of the following statements is true regarding resistors in series?
a) The total resistance is less than the smallest individual resistance.
b) The current through each resistor is different.
c) The voltage across the circuit is divided equally among the resistors.
d) The total resistance is the sum of the individual resistances.
Answer: d) The total resistance is the sum of the individual resistances.
Explanation: When resistors are connected in series, the total resistance of the circuit is equal to the sum of all the individual resistances.
Q15. If the current flowing through a resistor increases, what happens to the heat produced by the resistor?
a) It decreases.
b) It remains constant.
c) It increases.
d) It first increases then decreases.
Answer: c) It increases.
Explanation: According to Joule’s law of heating, the heat produced in a resistor is directly proportional to the square of the current flowing through it. Therefore, if the current increases, the heat produced will also increase.
Q16. What is the effect of increasing the voltage across a resistor while keeping its resistance constant?
a) The power dissipated by the resistor decreases.
b) The power dissipated by the resistor remains the same.
c) The power dissipated by the resistor increases.
d) The resistor’s resistance increases.
Answer: c) The power dissipated by the resistor increases.
Explanation: The power dissipated in a resistor can be calculated by the formula
=
2
/
P=V
2
/R, where
V is the voltage and
R is the resistance. If the voltage is increased while the resistance remains constant, the power dissipated by the resistor increases.
Q17. Which device is used to control the current in an electric circuit?
a) Resistor
b) Rheostat
c) Capacitor
d) Inductor
Answer: b) Rheostat
Explanation: A rheostat is a type of variable resistor used to control the current flowing through an electric circuit by changing the resistance.
Q18. In a parallel circuit with identical bulbs, what happens if one bulb burns out?
a) All other bulbs will also burn out.
b) The remaining bulbs will shine brighter.
c) The remaining bulbs will shine with the same brightness.
d) The circuit will stop conducting electricity.
Answer: c) The remaining bulbs will shine with the same brightness.
Explanation: In a parallel circuit, each component operates independently of the others. If one bulb burns out, the remaining bulbs will continue to shine with the same brightness because the voltage across each bulb remains unchanged.
Q19. Which of the following is not a factor on which the resistance of a wire depends?
a) The wire’s length
b) The wire’s cross-sectional area
c) The wire’s color
d) The material of the wire
Answer: c) The wire’s color
Explanation: The resistance of a wire depends on its length, cross-sectional area, and the material from which it is made, but not on its color.
Q20. What does an electric current’s direction indicate in a conventional circuit?
a) The flow of positive charges from high to low potential
b) The flow of negative charges from low to high potential
c) The flow of electrons from high to low potential
d) The physical direction in which wires are laid out
Answer: a) The flow of positive charges from high to low potential
Explanation: Conventionally, the direction of electric current is considered to be the direction in which positive charges would move, from higher to lower potential, opposite to the actual flow of electrons.
Q21. What is the primary purpose of using a fuse in an electrical circuit?
a) To step up the voltage
b) To reduce the resistance of the circuit
c) To protect the circuit from excessive current
d) To increase the current flow
Answer: c) To protect the circuit from excessive current
Explanation: A fuse is used in electrical circuits as a safety device that protects the circuit from damage due to excessive current by melting and breaking the circuit if the current exceeds a safe level.
Q22. Which of the following correctly describes the SI unit of resistivity?
a) Ohm-meter (
Ω
⋅
Ω⋅m)
b) Ohm (
Ω
Ω)
c) Ohm per meter (
Ω
/
Ω/m)
d) Ohm square meter per meter (
Ω
2
/
Ωm
2
/m)
Answer: a) Ohm-meter (
Ω
⋅
Ω⋅m)
Explanation: The resistivity of a material is expressed in ohm-meter (
Ω
⋅
Ω⋅m), representing the resistance of a conductor with specific dimensions.
Q23. In which scenario would you use a parallel circuit instead of a series circuit?
a) When you want all components to have the same voltage.
b) When you want each component to have a different voltage.
c) When you want the total resistance to be more than the highest individual resistance.
d) When you want to ensure that if one component fails, the entire circuit stops working.
Answer: a) When you want all components to have the same voltage.
Explanation: In a parallel circuit, all components are connected across the same two points and, therefore, have the same voltage applied to them, unlike in a series circuit.
Q24. What happens to the brightness of a bulb if the voltage across it is increased?
a) The brightness decreases.
b) The brightness remains unchanged.
c) The brightness increases.
d) The bulb turns off.
Answer: c) The brightness increases.
Explanation: The brightness of a bulb is related to the power it consumes, which increases with the square of the voltage across it. Therefore, if the voltage is increased, the brightness of the bulb also increases.
Q25. Which instrument is used to measure potential difference?
a) Ammeter
b) Voltmeter
c) Galvanometer
d) Rheostat
Answer: b) Voltmeter
Explanation: A voltmeter is specifically designed to measure the potential difference between two points in an electric circuit.
Q26. What is the equivalent resistance of two resistors of resistances 4 Ω and 6 Ω connected in parallel?
a) 10 Ω
b) 2.4 Ω
c) 5 Ω
d) 24 Ω
Answer: b) 2.4 Ω
Explanation: For resistors in parallel, the reciprocal of the total resistance is the sum of the reciprocals of the individual resistances. So,
1
/
total
=
1
/
4
+
1
/
6
1/R
total
=1/4+1/6, and solving for
total
R
total
gives 2.4 Ω.
Q27. The heating effect of electric current is used in which of the following devices?
a) Electric bulb
b) Refrigerator
c) Electric bell
d) All of the above
Answer: a) Electric bulb
Explanation: The heating effect of electric current is notably used in an electric bulb, where the filament heats up to emit light.
Q28. What does the slope of a V-I graph represent for a conductor?
a) Resistance
b) Conductance
c) Capacitance
d) Inductance
Answer: a) Resistance
Explanation: The slope of a voltage-current (V-I) graph for a conductor gives the resistance of the conductor, as per Ohm’s law
=
V=IR.
Q29. For a fixed resistance, if the voltage across it is halved, the power dissipated by the resistor will:
a) Be halved
b) Remain the same
c) Be quartered
d) Double
Answer: c) Be quartered
Explanation: The power dissipated in a resistor is given by
=
2
/
P=V
2
/R. Halving the voltage results in the power being reduced to a quarter of its original value.
Q30. Which of the following materials would likely have the highest resistivity?
a) Silver
b) Copper
c) Rubber
d) Aluminum
Answer: c) Rubber
Explanation: Rubber is an insulator and would have a much higher resistivity compared to conductors like silver, copper, and aluminum.
Q31. What is the main function of an electric fuse?
a) To increase current flow
b) To decrease voltage
c) To prevent excessive current flow
d) To store electrical energy
Answer: c) To prevent excessive current flow
Explanation: An electric fuse is designed to protect electrical circuits from damage caused by excessive current flow. It melts and interrupts the circuit if the current exceeds a specified limit.
Q32. If the length of a conductor is doubled while keeping its cross-sectional area constant, the resistance of the conductor will:
a) Remain unchanged
b) Double
c) Halve
d) Quadruple
Answer: b) Double
Explanation: The resistance of a conductor is directly proportional to its length. Therefore, doubling the length of the conductor, while keeping its cross-sectional area constant, will double its resistance.
Q33. Which of the following is true for resistors connected in series?
a) The voltage across each resistor is the same
b) The total resistance is less than the smallest individual resistance
c) The current through each resistor is the same
d) The total resistance is equal to the average of individual resistances
Answer: c) The current through each resistor is the same
Explanation: In a series circuit, the same current flows through each resistor, regardless of their individual resistances.
Q34. A device that converts electrical energy into mechanical energy is a:
a) Transformer
b) Capacitor
c) Generator
d) Electric motor
Answer: d) Electric motor
Explanation: An electric motor converts electrical energy into mechanical energy, typically used to drive mechanical loads.
Q35. The unit “kWh” stands for:
a) Kilowatt-hour
b) Kilo-watt-heating
c) Kilowatt-heat
d) Kelvin-watt-hour
Answer: a) Kilowatt-hour
Explanation: Kilowatt-hour (kWh) is a unit of energy representing the energy equivalent to a power consumption of one kilowatt for one hour.
Q36. In a parallel circuit, if one of the multiple paths is broken, the current will:
a) Stop flowing through the entire circuit
b) Continue to flow through the remaining paths
c) Decrease in the entire circuit
d) Increase in the remaining paths
Answer: b) Continue to flow through the remaining paths
Explanation: In a parallel circuit, each path operates independently. If one path is broken, the current will continue to flow through the remaining paths without stopping.
Q37. What is the effect of adding more batteries in series to an electric circuit?
a) The resistance of the circuit decreases
b) The voltage across the circuit increases
c) The voltage across the circuit decreases
d) The current through the circuit decreases
Answer: b) The voltage across the circuit increases
Explanation: Adding more batteries in series increases the total voltage available in the circuit, which can increase the current if the resistance remains constant.
Q38. Which property of a material determines whether it is a good conductor or insulator?
a) Ductility
b) Malleability
c) Resistivity
d) Density
Answer: c) Resistivity
Explanation: Resistivity is a material property that indicates how strongly the material opposes the flow of electric current. A low resistivity indicates a good conductor, while a high resistivity indicates an insulator.
Q39. What does an ammeter measure?
a) Voltage
b) Resistance
c) Current
d) Power
Answer: c) Current
Explanation: An ammeter is specifically designed to measure the electric current in a circuit.
Q40. In a circuit, if the voltage remains constant but the resistance doubles, the current will:
a) Remain constant
b) Double
c) Halve
d) Quadruple
Answer: c) Halve
Explanation: According to Ohm’s Law, current is inversely proportional to resistance for a constant voltage. Therefore, if the resistance doubles, the current will halve.
Q41. A light bulb is rated 60 W for a 120 V power supply. If it is used with a 240 V power supply, its power rating will:
a) Remain 60 W
b) Increase to 120 W
c) Decrease to 30 W
d) Increase to 240 W
Answer: d) Increase to 240 W
Explanation: The power
P is given by
=
2
/
P=V
2
/R. If the voltage is doubled and the resistance remains constant, the power will quadruple. However, without knowing the exact resistance of the bulb, the direct calculation cannot be performed, and the options provided do not accurately reflect this calculation. This question is based on a misunderstanding of power calculation principles, as doubling the voltage would actually quadruple the power according to
=
2
/
P=V
2
/R, assuming the bulb’s resistance remains constant. A correct interpretation would involve recalculating the power based on the new voltage while considering the bulb’s resistance, leading to a different answer.
Q42. What is the primary advantage of connecting electrical devices in parallel rather than in series?
a) Increases the total resistance
b) Each device can operate independently
c) Reduces the overall power consumption
d) Increases the voltage for each device
Answer: b) Each device can operate independently
Explanation: One of the primary advantages of connecting electrical devices in parallel is that each device can operate independently of the others. If one device fails, it does not affect the operation of the others.
Q43. The unit used to measure electric power is:
a) Joule
b) Coulomb
c) Ampere
d) Watt
Answer: d) Watt
Explanation: Electric power is measured in watts (W), which represents the rate at which electrical energy is used or generated.
Q44. Which of the following devices can be used to control the brightness of a light bulb?
a) Voltmeter
b) Ammeter
c) Rheostat
d) Transformer
Answer: c) Rheostat
Explanation: A rheostat is a type of variable resistor that can be used to control the current flowing through a circuit, thereby adjusting the brightness of a light bulb.
Q45. When two resistors, each of 4 ohms, are connected in parallel, the total resistance is:
a) 8 ohms
b) 4 ohms
c) 2 ohms
d) 0.5 ohms
Answer: c) 2 ohms
Explanation: For resistors in parallel, the total resistance can be found using the formula
1
/
=
1
/
1
+
1
/
2
1/R
total
=1/R
1
+1/R
2
. For two 4-ohm resistors in parallel,
1
/
=
1
/
4
+
1
/
4
=
1
/
2
1/R
total
=1/4+1/4=1/2, making
=
2
R
total
=2 ohms.
Q46. What is the primary function of a capacitor in an electric circuit?
a) To resist the flow of electric current
b) To store electrical energy in an electric field
c) To convert electrical energy into mechanical energy
d) To measure the electric current
Answer: b) To store electrical energy in an electric field
Explanation: A capacitor is a device that can store electrical energy in an electric field. It is commonly used in electronic circuits for various purposes, including filtering, buffering, and energy storage.
Q47. In a simple electric circuit, the component that provides the energy to move electrons is called the:
a) Resistor
b) Capacitor
c) Battery
d) Inductor
Answer: c) Battery
Explanation: A battery provides the necessary energy to move electrons through a circuit, acting as a source of electrical energy.
Q48. Which of the following is true when a 10-ohm resistor and a 20-ohm resistor are connected in series?
a) The total resistance is 30 ohms
b) The total resistance is less than 10 ohms
c) The total resistance is 15 ohms
d) The total resistance is more than 30 ohms
Answer: a) The total resistance is 30 ohms
Explanation: When resistors are connected in series, the total resistance is the sum of the individual resistances. Therefore, for a 10-ohm resistor and a 20-ohm resistor in series, the total resistance is
10
Ω
+
20
Ω
=
30
Ω
10Ω+20Ω=30Ω.