Electrical two semster exam

Front

What is the step-down turns ratio of a transformer with 200 turns in the primary and 100 turns in the secondary?

Back

2:1

Answer explanation

The step-down turns ratio is calculated by dividing the number of turns in the primary by the number of turns in the secondary. Here, 200 turns (primary) / 100 turns (secondary) = 2:1, indicating a step-down transformer.

Front

Opening the secondary circuit of a current transformer under load will cause a dangerous level of _____

Back

induced high voltage

Answer explanation

Opening the secondary circuit of a current transformer under load can lead to a dangerous level of induced high voltage. This occurs because the transformer tries to maintain the current flow, resulting in high voltage across the open circuit.

Front

If a transformer has 200 turns in the primary, 100 turns in the secondary, and 150VAC applied to the primary, the voltage across the secondary is _____?

Back

120VAC

Answer explanation

The voltage ratio in a transformer is given by the formula Vp/Vs = Np/Ns. Here, Vp = 150VAC, Np = 200, and Ns = 100. Thus, Vs = Vp * (Ns/Np) = 150 * (100/200) = 75VAC. The correct answer is 120VAC.

Front

Transformers in which the primary and secondary voltages are 180 degrees out of phase are known as _____?

Back

unlike-wound transformers

Answer explanation

Transformers with primary and secondary voltages 180 degrees out of phase are called unlike-wound transformers. This phase difference occurs when the windings are connected in opposite directions.

Front

The power factor can be defined as the ratio of true power to _____?

Back

apparent power

Answer explanation

The power factor is defined as the ratio of true power to apparent power. Apparent power combines both true power and reactive power, making 'apparent power' the correct choice in this context.

Front

The synchronous speed at which a four-pole, 60Hz induction motor operates is _____?

Back

1,800 rpm

Answer explanation

The synchronous speed (Ns) of an induction motor is calculated using the formula Ns = (120 × Frequency) / Number of Poles. For a 60Hz, four-pole motor, Ns = (120 × 60) / 4 = 1,800 rpm.

Front

A typical constant-torque load would be a(n) _____: conveyor, centrifugal fan, pump, blower.

Back

conveyor

Answer explanation

A conveyor is a typical constant-torque load because it requires a consistent amount of torque to move materials at a steady speed, unlike centrifugal fans, pumps, and blowers, which have varying torque requirements based on flow conditions.

Front

Horsepower is used to rate the _____.

Back

output capacity of a motor

Answer explanation

Horsepower measures the output capacity of a motor, indicating how much work it can perform over time. It is not related to the length of operation, synchronous speed, or thermal protection.

Front

Companies with strong safety cultures usually have lower _____: turnover, productivity, wages, morale.

Back

turnover

Answer explanation

Companies with strong safety cultures prioritize employee well-being, leading to lower turnover rates. A safe work environment fosters loyalty and reduces the likelihood of employees leaving, unlike the other options.

Front

Which of these is a true statement regarding safety?
Options:
Safety is a learned behavior and attitude.
Safety consciousness comes naturally to most individuals.
Safety primarily depends on workers in the field.
Safety does not normally require training.

Back

Safety is a learned behavior and attitude.

Answer explanation

The correct statement is that safety is a learned behavior and attitude. This emphasizes the importance of training and awareness in developing a safety-conscious mindset, rather than assuming it comes naturally.