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 safety precautions to be taken while handling electricity electric charge and electric current physics ohm's law current electricity

Many electrical appliances are earthed or grounded. Reason behind this

  1. to make electricity balance

  2. due to "g"

  3. protection against shock

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

In case of an earthed appliance, if there is any leakage of current or the line wire comes in contact with its body, then the current flows to the ground.

Multiple choice safety precautions to be taken while handling electricity electric charge and electric current physics ohm's law current electricity

The earth wire is connected to the outer casing of the appliance because ___________.

  1. The earth wire can prevent the fuse from blowing

  2. The earth wire can carry leaked charges to the ground

  3. The outer casing is an insulator and therefore it can store charges

  4. The earth wire can conduct the heat away from the appliance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance

Multiple choice safety precautions to be taken while handling electricity electric charge and electric current physics ohm's law current electricity

The earth wire is connected to the outer casing of the appliance because ...................  .

  1. The earth wire can prevent the fuse from blowing

  2. The earth wire can carry leaked charges to the ground

  3. The outer casing is an insulator and therefore it can store charges

  4. The earth wire can conduct the heat away from the appliance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The earth wire is connected to the outer casing of the appliance because the earth wire can carry leaked charges to the ground.The outer surface is usually made conducting and an earth wire takes the excess charge from the body to the earth which is a charge sink,thus preventing us from getting a shock due to charge buildup.

Multiple choice physics electric current through conductors combination of resistors combination of cells combinations of components

Two non ideal batteries are connected in series. Consider the following statements
(A) The equivalent emf is larger than either of the two emfs.
(B) The equivalent internal resistance is smaller than either of the two internal resistances.

  1. Both A and B are correct

  2. A is correct but B is wrong

  3. B is correct but A is wrong

  4. Both A and B wrong
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If we add two non ideal batteries in series then
so in case (a) the equivalent e.m.f.  may be larger than either of two e.m.f., but in case (b) the equivalent e.m.f. may be smaller than either of two e.m.f.
In series total resistance is always greater than individual resistance, whether batteries are connected in any way 

[i.e. either according to case (a) or case (b)].

Multiple choice physics electric current through conductors combination of resistors combination of cells combinations of components

When cells are connected in series greater emf is obtained in the circuit.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When two or more cells are connected in series in a circuit, the total potential difference is the sum of their potential differences. Hence, the cells are connected in series in order to produce a larger total emf.

Multiple choice physics electric circuits combination of resistors combination of cells combinations of components

Two non-ideal batteries are connected in series. Consider the following statements:
(A) The equivalent emf is larger than either of the two emfs.
(B) The equivalent internal resistance is smaller than either of the two internal resistances

  1. Each of A and B is correct

  2. A is correct but B is wrong

  3. B is correct but A is wrong

  4. Each of A and B is wrong
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When two non-ideal batteries are connected in series, their equivalent emf is
$E _{eq} = E _1 + E _2$
Hence, the equivalent emf is larger than either of the two emfs.
Also, their equivalent internal resistance is
$r _{eq} = r _1 + r _2$
Hence, the equivalent resistance is larger than either of the two internal resistances.
Therefore, statement A is correct but B is wrong.

Multiple choice physics simple electric circuits bulbs bulb bulb connected to an electric cell

A building has $10$ bulbs of $40W$, $5$ bulbs of $100W$, $5$ fans of SOW and one heater of $1$ kilowatt.Every day bulbs are using for $5$ hours, fans are using for $8$ hours and heater is using for $1$ hour. The electric mains voltage is $220 V$. Calculate:

  1. Maximum power of the electric circuit in the building

  2. The minimum capacity of main fuse in the building and
  3. The cost of consumed electric energy the rate of Rs $5$ per unit in a week

  4. Maximum power of the electric circuit in the building.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Daily energy: 10×40×5/1000 = 2 kWh (bulbs), 5×100×8/1000 = 4 kWh (fans), 1×1×1 = 1 kWh (heater). Total daily = 7 kWh. Weekly = 49 kWh. Cost at Rs 5/unit = Rs 245. Option C asks for the cost of consumed energy.

Multiple choice physics simple electric circuits bulbs bulb bulb connected to an electric cell

The filament of bulb offers ______ resistance to electric current.

  1. no

  2. low

  3. high

  4. very low
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The filament of bulb has high resistance so the filament heats up due to current passing through (${ I }^{ 2 }R$ losses )  and due to its heating , the electrons change their energy states and photons in visible spectrum are emitted . more the losses , more would be the light.that's why filament of bulb offers high resistance.

Multiple choice physics simple electric circuits bulbs bulb bulb connected to an electric cell

When current is passed through an electric bulb, its filament glows, but the wire leading current to the bulb does not glow because :

  1. Less current flows in the leading wire as compared to that in the filament

  2. The leading wire has more resistance than the filament

  3. The leading wire has less resistance than the filament

  4. Filament has coating of fluorescent material over it
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The leading wire is usually made with conductors such as copper and aluminium, therefore have less resistance than the filament which is usually made with tungsten and has a high resistance.
Due to this the power lost P $ =I^{2}R $ is greater for filament which is visible as light(and also heat).

Multiple choice physics simple electric circuits bulbs bulb bulb connected to an electric cell

The filament of a bulb is usually a

  1. Thin wire with many coils

  2. Thick wire with many coils

  3. Thin straight wire

  4. Thick strength wire
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Filaments in incandescent light bulbs are made of tungsten. When electric current goes through the filament, the filament glows. It may also be known as the electron emitting element in a vacuum tube. To make the bulb produce more light,the filament is usually made of coils of fine wire, also known as the coiled coil.

Multiple choice physics simple electric circuits bulbs bulb bulb connected to an electric cell

A 25W and 100W bulb are joined in series and connected to the mains. Which bulb will glow brighter?

  1. 25 W bulb

  2. 100 W bulb

  3. Both bulb will glow brighter

  4. None will glow brighter
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Resistance of 25 w bulb, ${R _1} \Rightarrow \frac{{{{220}^2}}}{2} = 1936\Omega $

$\begin{array}{l} { R _{ 2 } }=\frac { { { { 220 }^{ 2 } } } }{ { 100 } } =484\Omega  \ In\, \, series \ P\alpha R, \end{array}$
25 w will glow more

Multiple choice physics current electricity and magnetism electric bell the magnetic effect of a current electromagnetic forces oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

Which power supply can be used in electric bell

  1. $AC$
  2. $DC$

  3. Can't be predicted

  4. Both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Electric bell works on the mechanism of electromagnets and for this any type of power either AC or DC can be used.

Multiple choice physics current electricity and magnetism electric bell the magnetic effect of a current electromagnetic forces oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

When the switch of an electric bell is pushed

  1. Flow of the current stops through the electromagnet in the bell

  2. Current starts to flow through the electromagnet

  3. Voltage decreases in the current flowing through the electromagnet

  4. Circuit is closed in the electric bell
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
When the switch of an electric bell is pushed, current start to flow through the electromagnet.
When switch is pushed , circuit is closed and current starts flowing through the electromagnet in bell & bell starts ringing.
OPTION : B.