Physics

Electrical Machines and Circuits

754 Questions

Electrical machines and circuits involve the principles of alternating and direct current, transformers, diodes, and power consumption. These concepts are essential for engineering and technical exams. Review these practice questions to test your knowledge of circuit analysis.

Transformers and impedanceAlternating and direct currentCircuit components and diodesPower consumption calculations

Electrical Machines and Circuits Questions

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Which of the following statement about the action of a transformer is correct?

  1. Alternating current always flows in the secondary coil when an alternating voltage is applied to the primary coil.

  2. The current in the secondary coil is always larger than the current in the primary coil.

  3. An e.m.f. is induced in the secondary coil when an alternating voltage is applied to the primary coil.

  4. An e.m.f. is induced in the secondary coil when a steady direct current flows in the primary coil.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Alternating current does not flow in the secondary coil unless electrical load is connected to its terminals.
In step-up transformer current in secondary coil is less than the current in primary coil.
No e.m.f. is induced in the secondary coil if the primary coil is connected to a d.c. supply.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

The current drawn by the primary of a transformer, which steps down 200 V to 20 V to operate a device of resistance 20 $\Omega$ is: (Assume the efficiency of the transformer to be 80 %)

  1. 0.125 A

  2. 0.225 A

  3. 0.325 A

  4. 0.425 A
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$V _{primary} =200\ V$
$V _{secondary}=20\ V$
$R=20\ \Omega$
Power secondary $=\dfrac {(V _{secondary}^2)}{R}$

                               $=20\ W$

Power primary $=\dfrac {20}{\dfrac {80}{100}}=25\ w\quad (80\%\ efficiency)$

Power primary $=(I _{primary}) (V _{primary})$
$25=I _P \times 200$
$I _P=0.125\ A$
Option $(A)$
Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

In a step up transformer the turn ratio is 1:2. A Leclanche cell (emf = 1.5 V) is connected across the primary. The voltage across the secondary is

  1. 3.0 V

  2. 1.5 V

  3. 0.75 V

  4. 0
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For the step up transformer -

$\dfrac { { V } _{ 1 } }{ { V } _{ 2 } } =\dfrac { { n } _{ 1 } }{ { n } _{ 2 } } $

$\dfrac { 1.5 }{ { V } _{ 2 } } =\dfrac { 1 }{ 2 } $

$\Rightarrow { V } _{ 2 }=3V$.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

A transformer works on the principle of

  1. self induction

  2. electrical inertia

  3. mutual induction

  4. magnetic effect of the electrical current
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Transformer is based on the principle of electromagnetic induction.
There are two coils named as primary and secondary wound on a soft iron core.
When AC is applied to the primary coi, the resulting current will the production of
continously varying magnetic flux.
Due to mutual induction, induced EMF is produced in secondary coil which in return results in current.  
Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Transformer is used to

  1. convert ac to dc voltage

  2. convert dc to ac voltage

  3. obtain desired dc power

  4. obtain desired ac voltage and current
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Transformer converts some value of voltage/current into some other desired value based upon the principles of mutual induction.
Transformer is based on the principle of electromagnetic induction. There are two coils named as primary and secondary wound on a soft iron core. When AC is applied to the primary coil, the resulting current will the production of continuously varying magnetic flux. Due to mutual induction, induced EMF is produced in secondary coil which in return results in current.  

Multiple choice

What is the typical voltage of a lithium-ion camera battery?

  1. 1.2 volts

  2. 3.6 volts

  3. 9 volts

  4. 12 volts
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lithium-ion camera batteries typically have a nominal voltage of 3.6 volts, which provides sufficient power for the camera's operation.

Multiple choice

What is the typical voltage of a button cell camera battery?

  1. 1.2 volts

  2. 3.6 volts

  3. 9 volts

  4. 12 volts
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Button cell camera batteries typically have a nominal voltage of 1.2 volts, which is suitable for powering small electronic devices like cameras.

Multiple choice

What is the typical voltage of an action camera battery?

  1. 1.2 volts

  2. 3.6 volts

  3. 9 volts

  4. 12 volts
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Action camera batteries typically have a nominal voltage of 3.6 volts, which is suitable for powering the camera's high-performance features.

Multiple choice

What is the term used to describe the electrical device that regulates the flow of electricity to a light source?

  1. Ballast

  2. Transformer

  3. Capacitor

  4. Inductor
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Ballast is the term used to describe the electrical device that regulates the flow of electricity to a light source, ensuring proper operation and extending the lifespan of the light source.

Multiple choice

What is the most common type of electrical fault on a marine vessel?

  1. Short circuit

  2. Open circuit

  3. Ground fault

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Short circuits, open circuits, and ground faults are all common types of electrical faults that can occur on a marine vessel.

Multiple choice

What is the recommended procedure for replacing a faulty electrical component on a marine vessel?

  1. De-energize the circuit

  2. Lock out and tag the circuit

  3. Remove the faulty component

  4. Install the new component

  5. All of the above
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

When replacing a faulty electrical component on a marine vessel, it is important to de-energize the circuit, lock out and tag the circuit, remove the faulty component, and install the new component.

Multiple choice

What is the typical voltage of a lead-acid battery cell?

  1. 1.2 V

  2. 3.6 V

  3. 2.1 V

  4. 6 V
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The typical voltage of a lead-acid battery cell is approximately 2.1 volts. This value can vary slightly depending on the specific type of lead-acid battery and its state of charge.

Multiple choice

What is the recommended charging voltage for lead-acid batteries?

  1. 12.6 V

  2. 13.8 V

  3. 14.4 V

  4. 15.0 V
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The recommended charging voltage for lead-acid batteries is typically around 14.4 volts. Charging batteries at higher voltages can lead to overcharging, which can damage the battery and shorten its lifespan.

Multiple choice

What is the recommended discharge voltage for lead-acid batteries?

  1. 10.5 V

  2. 11.5 V

  3. 12.5 V

  4. 13.5 V
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The recommended discharge voltage for lead-acid batteries is typically around 10.5 volts. Discharging batteries below this voltage can lead to sulfation, which can damage the battery and reduce its capacity.