Which component opposes the change in current in a circuit?
A Resistor
B Capacitor
C Inductor
D Diode
An inductor opposes changes in current through it by generating a counter-electromotive force (EMF) according to Lenz’s Law.
What is the relationship between voltage and current in a purely resistive circuit?
A Voltage leads current by 90°
B Voltage lags current by 90°
C Voltage and current are in phase
D Voltage and current are out of phase
In a resistive circuit, voltage and current change simultaneously because resistance does not cause phase shifts.
Which of the following devices uses the principle of electromagnetic induction?
A Transformer
B Capacitor
C Resistor
D Battery
A transformer operates on the principle of electromagnetic induction to transfer electrical energy between two coils by mutual induction.
What is the unit of inductance?
A Farad
B Ohm
C Henry
D Watt
Inductance is measured in henries (H). One henry is the inductance when a current change of one ampere per second induces an EMF of one volt.
In a series RLC circuit, at resonance, the impedance is:
A Maximum
B Minimum
C Zero
D Infinite
At resonance, the inductive reactance and capacitive reactance cancel each other, leaving only the resistance, which is the minimum impedance in the circuit.
Which electrical symbol represents a resistor in a circuit diagram?
A A zigzag line
B A straight line
C A circle with a cross
D A rectangle
A resistor is represented by a zigzag line in circuit diagrams, indicating its role in resisting current flow.
Which of the following determines the polarity of an induced voltage in a conductor?
A Coulomb’s Law
B Faraday’s Law
C Lenz’s Law
D Ohm’s Law
Lenz’s Law states that the direction of induced EMF opposes the change in magnetic flux that caused it, determining polarity.
Which safety device detects and interrupts leakage currents to prevent electric shocks?
A Fuse
B Circuit Breaker
C Residual Current Device (RCD)
D Transformer
An RCD detects leakage currents caused by faults and quickly disconnects the circuit to protect users from electric shocks.
What is the main purpose of a step-down transformer?
A To increase current
B To reduce voltage
C To decrease power
D To improve resistance
A step-down transformer reduces the voltage level while increasing the current proportionally, maintaining the same power.
What is the total capacitance when capacitors are connected in series?
A Equal to the sum of individual capacitances
B Less than the smallest capacitance
C Equal to the largest capacitance
D Equal to the product of capacitances
In a series connection, the total capacitance is calculated using: \( 1/C_{\text{total}} = 1/C_1 + 1/C_2 + … \), resulting in a value less than the smallest individual capacitance.
What is the purpose of using a rheostat in a circuit?
A To measure voltage
B To vary resistance
C To amplify current
D To convert AC to DC
A rheostat is a variable resistor used to adjust current flow by changing the resistance in the circuit.
What is the main difference between AC and DC?
A AC flows in one direction, while DC reverses direction
B AC reverses direction periodically, while DC flows in one direction
C AC has higher voltage than DC
D DC is safer than AC
Alternating current (AC) changes direction periodically, whereas direct current (DC) flows steadily in a single direction.
Which of the following appliances typically uses a DC motor?
A Ceiling fan
B Vacuum cleaner
C Electric car
D Refrigerator
Electric cars use DC motors for their high efficiency and control over speed and torque.
What is the standard voltage level for residential wiring in most countries?
A 120V or 230V
B 12V or 24V
C 400V or 415V
D 600V or 1000V
Most residential systems use either 120V (e.g., USA) or 230V (e.g., Europe and India) depending on the country’s electrical standards.
Which component converts AC to DC in an electrical circuit?
A Diode
B Transformer
C Resistor
D Capacitor
A diode acts as a rectifier, allowing current to flow in one direction only, thus converting AC to DC.
Which factor affects the resistance of a conductor?
A Length
B Cross-sectional area
C Material
D All of the above
Resistance depends on the length, cross-sectional area, and material of the conductor, as described by the formula \( R = \rho \frac{L}{A} \), where \( \rho \) is resistivity.
What is the purpose of a multimeter?
A To measure current only
B To measure resistance only
C To measure multiple quantities like voltage, current, and resistance
D To measure temperature
A multimeter is a versatile device used to measure voltage, current, resistance, and sometimes other parameters.
What does the term “short circuit” mean?
A High resistance in the circuit
B A direct connection between two points of different potentials
C No current in the circuit
D A completely open circuit
A short circuit occurs when two points with different potentials are connected directly, leading to a high current flow and potential damage.
What is the efficiency of an ideal transformer?
A 0%
B 50%
C 100%
D Infinite
An ideal transformer has no losses, so all the input power is transferred to the output, giving it 100% efficiency.
Which device is used to detect the presence of electric fields?
A Voltmeter
B Galvanometer
C Electroscope
D Ammeter
An electroscope is used to detect the presence of electric charges or electric fields by observing the deflection of its metal leaves.