Physics

Electrical Machines and Circuits

720 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

A zener diode is specified as having a breakdown voltage of $9.1 V$, with a maximum power dissipation of $364 \ mW$. What is the maximum current the diode can handle? 

  1. $40 \ mA$
  2. $60 \ mA$
  3. $50 \ mA$
  4. $45 \ mA$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Maximum power dissipation is the product of breakdown voltage and maximum current. Dividing the maximum power by the Zener voltage yields I_max = P / V_z = 364 mW / 9.1 V = 40 mA. Thus, option A is the correct choice.

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

The color coding of  earth, live and neutral wire respectively is

  1. Green, Red, black

  2. Red, Green, Black

  3. Red, Black, Green

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The electric power line enters our house through three wires- namely the live wire, the neutral wire and the earth wire. To avoid confusion we follow a colour code for insulating these wires. The red wire is the live wire, and the black wire is neutral. The earth wire is given green plastic insulation.
The colour coding of wires is green for earth red for live and black for neutral.

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 transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

In a triode, $g$$ _m$ $= 2$ $\times$$ 10$$^{-3}$ $\Omega^{-1}$, $\mu$ $= 42$, resistance of load, $R = 50k\Omega$. The voltage amplification obtained from this triode will be

  1. $30.42$
  2. $29.57$
  3. $28.18$
  4. $27.15$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Voltage gain, $\displaystyle A _v = \beta \dfrac{R _L}{R _i} = 0.6 \times \dfrac{24}{3} = 4.8$

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

The grid voltage of any triode valve is changed from -1 volt to -3 volt and the mutual conductance is 3$\times$ 10$^{-4}$ mho. The change in plate circuit current will be

  1. 0.8 mA

  2. 0.6 mA

  3. 0.4 mA

  4. 1 mA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle g _m = \frac{\Delta I _p}{\Delta V _g}$

or $\Delta I _p = g _m \times \Delta V _g = 3 \times 10^{-4} \times [-3-(-1)]$
$= - 0.6 \times 10^{-3} A$ = shortage of $0.6 \times 10^{-3}A$

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

It is not safe to carry out electrical repair works outdoor during rain because :

  1. rainwater is a good conductor of electricity

  2. rainwater contains mineral salts

  3. rainwater is a poor conductor of electricity

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

It is not safe to carry out electrical repair works outdoor during rain because it contains small amounts of mineral salts naturally present in it. This water is thus a good conductor of electricity.

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

Alternating current is flowing in inductance L and resistance R. The frequency of source is $\displaystyle\frac{\omega}{2\pi}$. Which of the following statement is correct.

  1. For low frequency the limiting value of impedance is L
  2. For high frequency the limiting value of impedance is $L\omega$

  3. For high frequency the limiting value of impedance is R
  4. For low frequency the limiting value of impedance is $L\omega$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\begin{array}{l} \, \, As\, frequency\, approaches\, zero\, or\, DC,\, the\, inducators\, reac\tan  ce\, would\, decrease\, tozero\, , \ acting\, like\, a\, short\, circuit.\, this\, means\, inductive\, reac\tan  ce\, is\, proportional\, to\, fequency \ \, \, \, \, \, \, \, \, \, \, \, \, \, so\, ,\, for\, low\, frequency\, the\, { { limimiting } }\, \, value\, of\, impedance\, is\, L,\, and\, \, alternating\,  \ current\, is\, flowing\, in\, inductance\, L\, and\, resistance\, R.\, \, The\, frequency\, of\, source\, is\, \frac { \omega  }{ { 2\pi  } } . \ so\, the\, correct\, option\, is\, A. \end{array}$