# Objective Type Questions on Electrical Engineering

49) Which of the following has negative temperature coefficient ?

A. Brass

B. Mercury

C. Electrolyte

D. Silver

 A B C D

In general, carbon, all semiconductors, including germanium and silicon and also, all electrolyte solutions, such as sulfuric acid and water, have a negative temperature coefficient.

50) Which of the following has positive temperature coefficient ?

A. tungsten

B. dilute sulfuric acid

C. silicon

D. germenium

 A B C D

All metals in their pure form, such as copper, silver, aluminium and tungsten etc, have a positive temperature coefficient.

51) Resistance of which material does not change with change in temperature ?

A. platinum

B. Metal alloys Constantan and Manganin

C. brass

D. tungsten

 A B C D

Resistance is constant with changes in temperature in the metal alloy of constantan and manganin. This material has the temperature coefficient zero. They can be used for precision wire wound resistors, which do not change resistance when the temperature increased.

52) All of the following have negative temperature coefficient EXCEPT

A. paper

B. tungsten

C. germanium

D. rubber

 A B C D

All metals in their pure form, such as copper, silver, aluminium and tungsten etc, have a positive temperature coefficient.

53) The hot resistance of a tungsten lamp is about 10 times the cold resistance. Accordingly, cold resistance of a 100W, 200V lamp will be

A. 400 Ω

B. 40 Ω

C. 4 Ω

D. 800 Ω

 A B C D
$The\;resistance\; R = \frac{V^2}{W}$
Where, V is supply voltage and W is wattage rating of the lamp. Here, V = 200 V and W = 100 W,
$Therefore,\; hot\; resistance\; R = \frac{200^2}{100} = 400 \Omega$
∴ cold resistance of the lamp is 400 ⁄ 10 = 40 Ω

$54)\;For\; same\; voltage,\; the\; ratio\; \frac{Resistance\; of\; 100W\; lamp}{Resistance\; of\; 25w\; lamp}\;is$

A. 16

B. 4

C. 1/4

D. 1

 A B C D
$The\; resistance\; R\; = \frac{V^2}{W}$
Where, V is supply voltage and W is wattage rating of the lamp.
From, above equation it is clear that, for fixed voltage source, resistance of an electric lamp is inversely proportional to its wattage rating. That means, ratio of resistance will be just reverse of their ratio of wattage rating.

55) Which of the following has least resistivity

A. copper

C. mercury

D. Aluminium

 A B C D
Materials Resistivity at 20 oC
Copper 1.68 X 10 - 8 Ω - m
Lead 22 X 10 - 8 Ω - m
Mercury 98 X 10 - 8 Ω - m
Aluminium 2.65 X 10 - 8 Ω - m

56) Rating of fuse wire is expressed in

A. Watts

B. Mho

C. Ω

D. Ampere.

 A B C D

A fuse in electrical circuit is used to protect the circuit from over current and short circuit current. Actually fuse elements melt to disconnect the continuity when current beyond the predetermined value flows through them. So it is most appropriate to express the rating of fuse in Ampere.

57) Which of the following material is not used as fuse element

A. Silver

B. Copper

C. Aluminium

D. Carbon

 A B C D

The melting point of carbon is 3500oC. It is very difficult reach that high temperature when short circuit current flows through the fuse. Hence for short circuit or over current condition the fuse will not melt to disconnect the circuit if the fuse is made off carbon.

58) Which of the following lamp has least resistance ?

A. 200W, 220V

B. 100W, 220V

C. 60W, 220V

D. 25W, 220V

 A B C D
$The\; resistance\; R = \frac{V^2}{W}$
Where, V is supply voltage and W is wattage rating of the lamp.
From, above equation it is clear that, for fixed voltage source, resistance of an electric lamp is inversely proportional to its wattage rating.
Here, 200W, 220V lamp has highest wattage rating, therefore its resistance will be least.

59) Filaments of electric bulbs are generally made of

A. nichrome

B. tungsten

C. copper

D. carbon

 A B C D

Tungsten has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. When current flows through high resistive tungsten filament, it will not melt but glow. That is why filaments of electric bulbs are generally made of tungsten.

60) The value of supply voltage for 400W, 4 ohm load is

A. 40 V.

B. 400 V

C. 20 V

D. 200 V

 A B C D
$The\; resistance\; R = \frac{V^2}{W}$
Where, V is supply voltage and W is wattage rating of the lamp.
Here, W = 400W and R = 4Ω
$Putting \;theses\; values\; in\; the\; above\; equation,\; we\; get,\; 4\; = \frac{V^2}{400}$
⇒ V = 40V

61) Four resistance R1, R2, R3, & R4 are connected in series across a 220V supply. The resistances are such that, R1 > R2 > R3 > R4. The least power consumption will be in

A. R2

B. R4

C. R1

D. R3

 A B C D

$The\; current\; through\; the\; resistances,\; I = \frac{220V}{R_{1} + R_{2} + R_{3} + R_{4}}$
So the power consumed by the individual resistor will be I2R1, I2R2, I2R3 & I2R4
As, R1 > R2 > R3 > R4
I2R1 > I2R2 > I2R3 > I2R4

62) 200 resistors of 200 Ω each are connected in parallel. Their equivalent resistance will be

A. 1 Ω

B. 200 Omega;

C. 400 Omega;

D. 4 kΩ

 A B C D

If N numbers of resistors of RΩ each are connected in parallel. Their equivalent resistance will be R ⁄ N

63) The resistance of 100W, 200V lamp is

A. 200 Ω

B. 400 Ω

C. 800 Ω

D. 1600 Ω

 A B C D

$The\; resistance\; R = \frac{V^2}{W}$
Where, V is supply voltage and W is wattage rating of the lamp.
Here, wattage of the lamp W = 100W, and supply voltage V = 200V
$The\; resistance\; R = \frac{200^2}{100} = 400 \Omega$

64) A 1 kΩ, 1W resistor can safely pass a current of

A. 30 mA

B. 60 mA

C. 40 mA

D. 100 mA

 A B C D

The wattage rating of the resistor W = I2.R
Here W = 1 W, R = 1 kΩ = 1000 Ω
∴ I = √(1/1000) = 0.0316 A = 31.6 mA > 30 mA

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