Basic Electrical and Electronics Engineering: 18 MCQs with answers

Voltage is the cause (potential difference); current is the effect (flow of charge).

Voltage is the potential difference that drives charge, while current is the actual rate of flow of charge. A 12 V battery with nothing connected has voltage but zero current.

$V = IR$

Ohm's law states $V = IR$ at constant temperature. The other forms are algebraic rearrangements or unrelated expressions.

$3\ \text{A}$

Using $I = V/R = 12/4 = 3\ \text{A}$.

Ohm ($\Omega$)

Resistance is measured in ohms ($\Omega$). Volts measure voltage, amperes measure current, and watts measure power.

Current

In a series circuit, the same current flows through every component; the voltage splits across them.

A one-way valve for current

A diode conducts in one direction only, acting like a one-way valve. This property is used for rectification.

True

**Ohm's law** ($V = IR$) holds only when the temperature of the conductor is constant; filament bulbs and diodes violate it under normal operating conditions.

$0.6\ \text{kWh}$

Energy $E = Pt = 60\ \text{W} \times 10\ \text{h} = 600\ \text{Wh} = 0.6\ \text{kWh}$.

$2\ \Omega$

$\frac{1}{R_{eq}} = \frac{1}{6} + \frac{1}{3} = \frac{1}{2}$, so $R_{eq} = 2\ \Omega$.

It becomes four times the original value.

$R = \rho L / A$. Doubling $L$ doubles $R$; halving $A$ doubles $R$ again. Combined effect: $R$ becomes $4\times$.

So each appliance gets the full supply voltage and can be switched independently.

Parallel connection gives each appliance the full supply voltage and allows independent switching. In series, one failed component breaks the whole circuit.

The positive terminal of the supply is connected to the p-side.

Forward bias means the p-side is connected to the positive terminal and the n-side to the negative terminal, allowing current to flow.

Heating effect, since $P = I^2R$ melts the fuse wire.

A fuse relies on the heating effect of current. When current exceeds a safe value, $P = I^2R$ generates enough heat to melt the fuse wire.

For metals, resistance increases with temperature, so the hot filament has higher resistance.

Ohm's law holds only at constant temperature. For most metals, resistance rises with temperature, so the glowing filament has much higher resistance than the cold one.

It rectifies both halves of the AC cycle, giving full-wave output.

A single diode gives half-wave rectification (one half of the cycle is blocked). Four diodes in a bridge configuration rectify both halves, producing full-wave DC.

Amplification of weak signals

A small base current controlling a large collector current is the principle of amplification. Rectification is done by diodes; voltage stepping is done by transformers.

1.5 A

Using Ohm's law, the initial resistance can be calculated as $R = \frac{V}{I} = \frac{12 V}{3 A} = 4 \Omega$. If the resistance is doubled, the new resistance becomes $8 \Omega$. The new current can be calculated as $I = \frac{V}{R} = \frac{12 V}{8 \Omega} = 1.5 A$.

3 \Omega

The equivalent resistance for resistors in parallel is given by the formula: $$\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$$. Substituting the values, we get: $$\frac{1}{R_{eq}} = \frac{1}{4} + \frac{1}{6} + \frac{1}{12} = \frac{3}{12} + \frac{2}{12} + \frac{1}{12} = \frac{6}{12} = \frac{1}{2}$$. T…