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 zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

If the load resistance decreases in a zener regulator, the zener current

  1. Decreases

  2. Stays the same

  3. Increases

  4. Equals the source voltage divided by the series resistance
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The load current is given by $I _L=\dfrac{V _z}{R _L}$ and the zener current is given by $I _z=I _s-I _L$. Thus, if the load resistance decreases, load current increases. This in turn will reduce the zener current 

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Which of the following is not true for wire wound resistor?

  1. It has a lower order of stability and reliability.

  2. It has high power rating with a low tolerance value.

  3. Easy to make wire wound resistor of value 0.01 Ohm.

  4. It is not suitable for high-frequency circuits.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
A wire wound resistor is an electrical passive component that limits current. The resistive element exists out of an insulated metallic wire that is winded around a core of non-conductive material. The wire material has a high resistivity, and is usually made of an alloy such as Nickel-chromium (Nichrome) or a copper-nickel-manganese alloy called Manganin. Common core materials include ceramic, plastic and glass. 
It has a lower order of stability and reliability  is not true for wire wound resistor
Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Which of the following is not the disadvantage of wire wound resistor?

  1. It has a big size which is not suitable for many of the applications.

  2. It has high power rating with a low tolerance value.

  3. Resistance value gets changed by a change in temperature, humidity etc.

  4. It is not suitable for high-frequency circuits.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In wired resistors are mainly produced with alloys, since pure metal has a high temperature co-efficient.

Due to alloy temperature co-efficient of wire wound resistor is very low.
Therefore it is very less effected by temperature change.

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Which of the following is true for carbon resistors?

  1. Resistance value does not get changed by change in temperature
  2. Current carrying capacity and hence power wattage are limited to about $50$ Watts.

  3. It has low-temperature coefficient value.

  4. Stability and reliability are very good.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$A\rightarrow$ Resistance value of carbon resistor with change in temperature it has negative thermal coefficient.

$B\rightarrow$ Carbon resistors are not current carrying capacitor.
$C\rightarrow$ Carbon has low temperature coefficient value i.e. higher the temperature, lower the resistivity.
$D\rightarrow$ Because of low stability of resistance value this type of resistors are not suitable.

Multiple choice physics work and energy commercial unit of energy power work and power

If 1 unit of electricity cost $0.20$, how much does it cost to switch on a heater marked $120 V$, $3 A$ for $90$ min?

  1. $ 0.11$
  2. $ 2.70$
  3. $ 64.80$
  4. $ 108.00$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Voltage across the heater $V = .12$ kilo-volts 
Current flowing through the heater $I = 3 A$
Thus power of the heater $P = VI$
$\therefore$ $P = 0.12 \times 3 = 0.36 $ $kW$
Time of operation $t = 90$ min $ = 1.5 $ hr
Thus energy consumed $E = Pt$
$\implies$ $E = 0.36 \times 1.5 = 0.54$ $kWhr$
Cost to switch on heater =  $0.54 \times 0.2 = 0.11$
Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

Which of the following devices can be used to detect a weak current?

  1. Use of electric bulb in tester.

  2. Use of LED in tester.

  3. A tester using magnetic effects of current.

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

LED glows even when a weak electric current flows through it. Also, even if the current is small, the deflection of the magnetic needle can be seen. Hence, tester using LED and magnetic effects of current can be used to detect a weak current.

Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

Which of the following might be the reason that the current in the circuit is weak?

  1. Circuit of the tester might not be complete.

  2. The material may not be able to conduct electricity as easily as metals.

  3. The circuit of the tester is complete but still the bulb does not glow.

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

Though a material may conduct electricity, it may not conduct it as easily as a metal. As a result, the circuit of the tester may be complete and yet the current through it may be too weak to make the bulb glow.

Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

What happens when the current passing through the circuit is too weak?

  1. The filament does not get heated sufficiently and the bulb does not glow.

  2. The filament gets heated but the bulb does not glow.

  3. The filament does not get heated but the bulb glows.

  4. The filament gets heated and the bulb glows.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the current through the circuit is too weak, the filament does not get heated sufficiently and the bulb does not glow.

Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

Which of the following statement(s) is correct while conducting electricity through vegetable oil?

  1. The liquid (vegetable oil) allows the electric current to pass through. Since, it is a good conductor of electricity.

  2. The circuit of the tester is complete but the bulb does not glow.

  3. The circuit of the tester is not complete and hence the bulb does not glow.

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

When the liquid (vegetable oil) does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.

Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

When electric current passes through the filaments of a bulb, it starts emitting light due to :

  1. heating effect of electric current.

  2. magnetic effect of electric current.

  3. chemical effect of electric current.

  4. lighting effect of electric current.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When electric current passes through the filaments of bulb, it starts emitting light due to heating effect of electric current.