What happens to the current in a circuit if the resistance is doubled while the voltage remains constant?
A Current doubles
B Current remains the same
C Current is halved
D Current becomes zero
According to Ohm’s Law, I = V/R. If R doubles, the current I is reduced to half while the voltage V remains constant.
Which device is used to step up or step down AC voltage?
A Generator
B Transformer
C Rectifier
D Motor
A transformer works on the principle of electromagnetic induction to increase (step-up) or decrease (step-down) the AC voltage.
What is the function of an Earth Leakage Circuit Breaker (ELCB)?
A To prevent overcurrent
B To detect ground faults
C To control voltage fluctuations
D To reduce resistance
ELCB detects leakage currents to the ground and disconnects the power supply to prevent electric shocks and fire hazards.
In a capacitor, the energy is stored in:
A Magnetic field
B Electric field
C Resistance
D Inductance
A capacitor stores energy in the form of an electric field created between its plates when a voltage is applied.
Which law states that the total current entering a junction equals the total current leaving it?
A Ohm’s Law
B Kirchhoff’s Current Law
C Faraday’s Law
D Lenz’s Law
Kirchhoff’s Current Law (KCL) states that the sum of currents entering a junction equals the sum of currents leaving it, ensuring charge conservation.
What is the primary purpose of a fuse in an electrical circuit?
A To measure current
B To regulate voltage
C To protect against overcurrent
D To store energy
A fuse protects a circuit by breaking the connection when the current exceeds a safe limit, preventing damage to devices and wiring.
What does an oscilloscope measure?
A Resistance
B Voltage over time
C Capacitance
D Magnetic field
An oscilloscope displays voltage signals as waveforms over time, helping analyze variations in AC and DC signals.
What is the purpose of a commutator in a DC motor?
A To generate power
B To reverse the direction of current
C To reduce resistance
D To step up voltage
The commutator reverses the current direction in the armature winding, ensuring continuous rotation of the DC motor.
What is the unit of electric power?
A Joule
B Watt
C Volt
D Ampere
Electric power is measured in watts (W). One watt equals one joule of energy consumed per second.
What is the main difference between a series circuit and a parallel circuit?
A Current is the same in all components of a series circuit
B Voltage is the same in all components of a series circuit
C Current is different in all components of a series circuit
D Voltage is different in all components of a parallel circuit
In a series circuit, the same current flows through all components because there is only one path for current flow.
What type of current does a battery produce?
A Alternating Current (AC)
B Direct Current (DC)
C Pulsating Current
D No current
A battery produces direct current (DC), where the flow of electric charge is unidirectional.
Which of the following is an ohmic conductor?
A Semiconductor
B Filament lamp
C Copper wire
D Diode
Ohmic conductors, like copper, follow Ohm’s Law, where the current is directly proportional to voltage, provided the temperature is constant.
What is the main disadvantage of an open circuit?
A Infinite resistance
B No current flow
C High power consumption
D Overcurrent
In an open circuit, there is a break in the connection, preventing current flow and rendering the circuit non-functional.
Which instrument is used to measure very high resistances?
A Ammeter
B Megger
C Voltmeter
D Multimeter
A megger is used to measure high resistances, typically in insulation testing of electrical equipment.
What is the primary role of an electric motor?
A To convert electrical energy into mechanical energy
B To convert mechanical energy into electrical energy
C To store energy
D To regulate voltage
An electric motor transforms electrical energy into mechanical energy, driving machines or devices like fans and pumps.
Which phenomenon is responsible for the working of an electric bell?
A Capacitance
B Electromagnetism
C Inductance
D Thermal effect
An electric bell uses electromagnetism to create a magnetic field, which moves a striker to hit the bell repeatedly.
What happens to the brightness of a bulb if its filament resistance increases?
A Brightness increases
B Brightness decreases
C Brightness remains the same
D The bulb explodes
As resistance increases, current decreases (by Ohm’s Law), resulting in reduced power and brightness.
What is the function of a rectifier in an electrical circuit?
A To amplify voltage
B To convert AC to DC
C To store charge
D To decrease resistance
A rectifier converts alternating current (AC) to direct current (DC) using diodes, making it suitable for devices requiring DC.
What causes a thermal effect in electrical circuits?
A Inductance
B Resistance
C Capacitance
D Voltage drop
The thermal effect occurs due to resistance, which converts electrical energy into heat as current flows through the circuit.
What is the standard frequency of AC supply in India?
A 50 Hz
B 60 Hz
C 100 Hz
D 25 Hz
The standard frequency of AC supply in India is 50 Hz, meaning the current changes direction 50 times per second.
What is the function of a circuit breaker in an electrical system?
A To measure voltage
B To convert AC to DC
C To interrupt current flow during overload or short circuit
D To step up the voltage
A circuit breaker automatically breaks the circuit when the current exceeds a safe limit, protecting devices and preventing hazards.
What type of current is produced by a solar cell?
A Alternating Current (AC)
B Direct Current (DC)
C Pulsating Current
D Static Current
A solar cell generates direct current (DC) as it produces electricity through the photovoltaic effect.
What is the main characteristic of a parallel circuit?
A Voltage is the same across all components
B Current is the same through all components
C Resistance remains constant
D Power is equal across all components
In a parallel circuit, all components share the same voltage as they are connected across the same potential difference.
What is the relationship between frequency and time period in an AC circuit?
A f = T
B f = 1/T
C f = T²
D f = 2T
The frequency (f) of an AC signal is the reciprocal of its time period (T): f = 1/T.
Which material is used as the core in an electromagnet?
A Aluminum
B Copper
C Iron
D Plastic
Soft iron is commonly used as the core in electromagnets because it enhances the magnetic field strength and is easily magnetized and demagnetized.
What is the power factor in a purely inductive circuit?
A 1
B 0
C -1
D 0.5
In a purely inductive circuit, the voltage and current are 90° out of phase, resulting in a power factor of zero as Power Factor = cos(90°) = 0.
What is the primary function of a capacitor in an electrical circuit?
A To store energy
B To measure current
C To increase resistance
D To step up voltage
A capacitor stores energy in the form of an electric field between its plates when a voltage is applied across it.
What is the equivalent resistance when two resistors of 10 ohms each are connected in parallel?
A 5 ohms
B 10 ohms
C 20 ohms
D 0.5 ohms
The equivalent resistance of resistors in parallel is given by 1/R_eq = 1/R1 + 1/R2. For two 10-ohm resistors, R_eq = 5 ohms.
What is the primary cause of electrical shock?
A High voltage
B High resistance
C Current flowing through the body
D Low voltage
Electrical shock occurs when current passes through the body, which can cause injury or even death depending on the magnitude.
Which device measures electrical resistance?
A Voltmeter
B Ohmmeter
C Ammeter
D Wattmeter
An ohmmeter is designed to measure the electrical resistance in a circuit or component.
What happens to the inductive reactance if the frequency of the AC supply is increased?
A It decreases
B It remains constant
C It increases
D It becomes zero
Inductive reactance (\( X_L = 2 \pi f L \)) is directly proportional to the frequency (\( f \)) of the AC supply. As frequency increases, the inductive reactance also increases.
Which type of motor is commonly used in ceiling fans?
A DC motor
B Synchronous motor
C Induction motor
D Stepper motor
Single-phase induction motors are commonly used in ceiling fans due to their simplicity, reliability, and cost-effectiveness.
What is the SI unit of magnetic flux?
A Weber
B Tesla
C Ampere
D Henry
The SI unit of magnetic flux is the weber (Wb), which represents the total magnetic field passing through a surface.
What is the purpose of a load in an electric circuit?
A To supply power
B To consume power
C To store energy
D To measure current
A load is any device or component in a circuit that consumes electrical power, such as a bulb, motor, or heater.
What does a galvanometer measure?
A Voltage
B Current
C Electric charge
D Direction of current
A galvanometer is a sensitive instrument used to detect and indicate the direction and magnitude of small currents.
In a transformer, what causes energy loss due to the resistance of the winding?
A Hysteresis loss
B Eddy current loss
C Copper loss
D Core loss
Copper loss occurs in a transformer due to the resistance of the windings, leading to heat generation when current flows.
What is the unit of electrical conductance?
A Siemens
B Ohm
C Ampere
D Volt
Electrical conductance is measured in siemens (S) and represents the reciprocal of resistance (\( G = 1/R \)).
What is the total power in a balanced three-phase system?
A P = V × I
B P = √3 V I cos φ
C P = 3 V I cos φ
D P = V/I
The total power in a balanced three-phase system is given by \( P = √3 V I cos φ \), where \( V \) is line voltage, \( I \) is line current, and \( cos φ \) is the power factor.
What type of circuit is used in household electrical wiring?
A Series circuit
B Parallel circuit
C Series-parallel circuit
D Open circuit
Household wiring is done in parallel to ensure each appliance receives the same voltage and operates independently.
What is the effect of an electric current passing through a conductor on a magnetic compass nearby?
A No effect
B The needle deflects
C The needle vibrates
D The needle becomes magnetized
When electric current flows through a conductor, it produces a magnetic field, causing the needle of a nearby magnetic compass to deflect.
What is the main purpose of an electric fuse?
A To store energy
B To increase current
C To protect appliances from overcurrent
D To convert AC to DC
An electric fuse contains a thin wire that melts and breaks the circuit when the current exceeds a safe limit, preventing damage to devices and potential hazards.
Which law relates the voltage, current, and resistance in an electrical circuit?
A Kirchhoff’s Voltage Law
B Ohm’s Law
C Faraday’s Law
D Lenz’s Law
Ohm’s Law states that \( V = IR \), where \( V \) is voltage, \( I \) is current, and \( R \) is resistance.
What type of conductor does not obey Ohm’s Law?
A Ohmic conductor
B Non-ohmic conductor
C Ideal conductor
D Pure conductor
Non-ohmic conductors, such as diodes and transistors, do not have a linear relationship between voltage and current and therefore do not follow Ohm’s Law.
What does an electric motor convert?
A Electrical energy into thermal energy
B Mechanical energy into electrical energy
C Electrical energy into mechanical energy
D Chemical energy into electrical energy
Electric motors transform electrical energy into mechanical energy, enabling the operation of various machines and devices.
Which quantity remains constant in a parallel circuit?
A Current
B Resistance
C Voltage
D Power
In a parallel circuit, all components share the same voltage, as they are connected across the same potential difference.
What is the unit of electrical resistance?
A Ampere
B Coulomb
C Ohm
D Volt
Electrical resistance is measured in ohms (Ω), which quantifies how much a material opposes the flow of electric current.
What happens to the total resistance when resistors are connected in series?
A It increases
B It decreases
C It remains constant
D It becomes zero
In a series connection, the total resistance is the sum of all individual resistances: \( R_{\text{total}} = R_1 + R_2 + R_3 \).
Which type of transformer increases voltage?
A Step-down transformer
B Step-up transformer
C Isolation transformer
D Autotransformer
A step-up transformer increases the input voltage by using a higher number of turns in the secondary coil than in the primary coil.
What is the primary function of a rectifier?
A To increase resistance
B To convert DC to AC
C To convert AC to DC
D To step up voltage
A rectifier uses diodes to convert alternating current (AC) to direct current (DC), which is used in various electronic devices.
Which component is used to store charge in an electrical circuit?
A Resistor
B Inductor
C Capacitor
D Transformer
A capacitor stores electrical energy in the form of an electric field between its plates when a voltage is applied.