1.1 Ohm's law states that the current flowing through a conductor is directly proportional to the:
Correct Answer: b) Voltage across it
Explanation: Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them. Mathematically: V = IR.
1.2 The SI unit of resistance is:
Correct Answer: c) Ohm
Explanation: The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm.
1.3 Which of the following factors does NOT affect the resistance of a conductor?
Correct Answer: d) Voltage applied
Explanation: Resistance of a conductor depends on its material (resistivity), length, cross-sectional area, and temperature. The applied voltage affects the current flow but not the inherent resistance of the conductor.
2.1 Kirchhoff's Current Law (KCL) is based on the principle of:
Correct Answer: c) Conservation of charge
Explanation: Kirchhoff's Current Law states that the algebraic sum of currents entering a node is zero. This is based on the principle of conservation of electric charge - charge cannot be created or destroyed at a node.
2.2 Kirchhoff's Voltage Law (KVL) states that the algebraic sum of voltages in a closed loop is:
Correct Answer: c) Equal to zero
Explanation: Kirchhoff's Voltage Law states that the sum of all electrical potential differences (voltages) around any closed network is zero. This is based on the principle of conservation of energy.
3.1 The unit of inductance is:
Correct Answer: a) Henry
Explanation: The henry (symbol: H) is the SI derived unit of inductance. It is named after Joseph Henry, the American scientist who discovered electromagnetic induction independently of Michael Faraday.
3.2 In a purely inductive circuit, the current:
Correct Answer: a) Lags the voltage by 90°
Explanation: In an inductive circuit, the current lags the voltage by 90° because the inductor opposes changes in current. Energy is first stored in the inductor's magnetic field before current can flow.
3.3 Capacitive reactance is given by:
Correct Answer: a) XC = 1/(ωC)
Explanation: Capacitive reactance (XC) is inversely proportional to both the frequency (ω = 2πf) and the capacitance (C). The formula is XC = 1/(ωC) = 1/(2πfC).
4.1 In an AC circuit, the power factor is the ratio of:
Correct Answer: b) Active power to apparent power
Explanation: Power factor (PF) is defined as the ratio of the real power (active power) flowing to the load to the apparent power in the circuit. PF = P/S = cos(θ), where θ is the phase angle between voltage and current.
4.2 In a purely capacitive AC circuit, the current:
Correct Answer: b) Leads the voltage by 90°
Explanation: In a capacitive circuit, the current leads the voltage by 90° because the capacitor must first charge up before a voltage can develop across it. Current flows immediately when voltage is applied, while voltage builds up as charge accumulates.
5.1 Which of the following is NOT a unit of power?
Correct Answer: b) Joule
Explanation: The joule is a unit of energy, not power. Power is the rate of energy transfer, measured in watts (or horsepower, kilowatts). 1 watt = 1 joule/second.
5.2 Electrical energy is measured in:
Correct Answer: a) Joules
Explanation: Electrical energy is the capacity to do work and is measured in joules (J). In practical terms, electrical energy is often measured in kilowatt-hours (kWh) for billing purposes (1 kWh = 3.6×106 J).