Practice MCQ Questions and answers on Physics-GK

71

Which of the following represents a relation for ''heat lost = heat gained'?

A) Principle of thermal equilibrium B) Principle of colors C) Principle of calorimetry D) Principle of vaporization

Discuss

Answer & Solution

Answer: Option C

Solution:

The answer is calorimetry, calorimetry is the principle used in calorimeters according to this the net rate of heat generated is same as heat gained by the cooling mechanism. Since there is no work transfer it is relevant.

72

Q = mcdT refers to

A) Enthalpy formula B) Heat Transfer formula C) Specific Heat formula D) Heat of Vaporization

Discuss

Answer & Solution

Answer: Option C

Solution:

Q = mcdT refers to Specific Heat formula.

73

Steam at 100°C causes more severe burns than water at 100°C because

A) Steam has no specific heat capacity B) Steam has latent heat of vaporisation C) Water has no specific heat capacity D) Water has latent heat of fusion

Discuss

Answer & Solution

Answer: Option B

Solution:

Steam will produce more severe burns than boiling of water because steam has more heat energy than water due to its latent heat of vaporisation and additionally latent heat of condensation.

74

No current will flow between two charged bodies if they have the same

A) Resistance B) Charge C) Potential D) Charge/ potential ratio

Discuss

Answer & Solution

Answer: Option C

Solution:

There is no current flows between two charged bodies connected together when they have the same potential. For the flow of current between two conductors is that there must be a potential difference. Only then the electrons can flow from a higher potential to a lower potential.

75

Two metallic wires made from copper have same length but the radius of wire 1 is half of that of wire 2. The resistance of wire 1 is R. If both the wires are joined together in series, the total resistance becomes

A) 2R B) R/2 C) 5R/4 D) 3R/4

Discuss

Answer & Solution

Answer: Option C

Solution:

So, resistance of Wire 2 is R/4 as radius is half of wire 1, so area would be 4 times of wire 1.
Now for resistance in series. R= R1 + R2.
Therefore, Final R= R + R/4 = 5R/4

76

Find the resistance (in mega) of a wire of length 20m, cross sectional area 1 cm² and made of a material of resistivity 200m.

A) 40 B) 4000 C) 80 D) 2000

Discuss

Answer & Solution

Answer: Option A

No explanation is given for this question. Let's Discuss on Board

77

A copper wire of radius r and length l has a resistance of R. A second copper wire with radius 2r and length l is taken and the two wires are joined in a parallel combination. The resultant resistance of the parallel combination of the two wires will be

A) 5 R B) 5 R/4 C) 4 R/5 D) R/5

Discuss

Answer & Solution

Answer: Option D

Solution:

1st copper wire: R = pl/A = pl/ πr2
2ndcopper wire: R’ = p’l’/A’ = pl/(4 πr2) = R/4
If joined in parallel, (1/Req) = (1/R) + (1/R’)
= 1/R + 4/R
= 5/R
Req = R/5

78

Which of the following is a good conductor of heat but a bad conductor of electricity ?

A) Celluloid B) Rubber C) Asbestos D) Mica

Discuss

Answer & Solution

Answer: Option D

Solution:

Mica is a good conductor of heat but bad conductor of electricity.

79

When a number of resistors are connected in series in a circuit, the value of current:

A) Increases B) Becomes half C) Decreases D) Remains the same

Discuss

Answer & Solution

Answer: Option D

Solution:

The same current flows through each resistor in series. Individual resistors in series do not get the total source voltage, but divide it. The total resistance in a series circuit is equal to the sum of the individual resistances: RN(series)=R1+R2+R3+… +RN.

80

A good conductor while carrying current is

A) Alternately charged positive and negative B) Negatively charged C) Positively charged D) Electrically neutral

Discuss

Answer & Solution

Answer: Option B

Solution:

Electrons carry current in a good conductor of electricity and they are negatively charged. This makes a good electrical conductor negatively charged.