Physics Test

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Physics Test - 14

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Question 1
1 / -0

A body constrained to move in y-direction is subjected to a force $F=2 \hat{i}+15 \hat{j}+6 \hat{k} N$. The work done by this force in moving the body through a distance of 10 m along the y-axis is

A
100 J

B
150 J

C
120 J

D
200 J

Solution

Work done $=\vec{F} \cdot \vec{r}=(2 \hat{i}+15 \hat{j}+6 \hat{k}) \cdot(10 \hat{j})=150 J$
Question 2
1 / -0

If there is a straight line parallel to volume axis in a P-V diagram, then it is an ____ graph.

A
isochoric

B
isobaric

C
isothermal

D
None of these

Solution

If there is a straight line parallel to volume axis in a P-V diagram, then it is an isobaric graph.
Isobaric- constant pressure
Isochoric- constant volume
Question 3
1 / -0

A gas is taken through a number of thermodynamic states. What happens to its specific heat?

A
It is always constant.

B
It increases.

C
It decreases.

D
It can have any value depending upon the process of heat absorbed or evolved.

Solution

The specific heat of a gas depends upon the process and can have any value as specific heat at constant volume is (C_v) and at constant pressure is (C_p).
Question 4
1 / -0

The figure below shows the P-V diagram for a fixed mass of an ideal gas undergoing cyclic process ABCA. AB represents an isothermal process.

Which of the following graphs represents the P-T diagram of the cyclic process?

A

B

C

D

Solution
Question 5
1 / -0

During the adiabatic expansion of 2 moles of a gas, the internal energy was found to have decreased by 100 J. The work done by the gas in this process is

A
zero

B
- 100 J

C
200 J

D
100 J

Solution

Using first law of thermodynamics ,
we have dU= -100 J
$d Q-d W=d U$
For adiabatic process
we have $d Q=0$,
thus $d W=-d U=100 \mathrm{J}$
Question 6
1 / -0

A lens produces an image of an object on a screen. If a slab of refractive index 'n' is placed between the lens and the screen, the screen has to be moved behind by distance 'd'. The thickness of the slab is

A
nd

B
$\frac{n-1}{n d}$

C
$\frac{(n-1) d}{n}$

D
$\frac{n d}{n-1}$

Solution

Shift in the position of image after introducing slab,
$(d)=t\left(1-\frac{1}{n}\right)$
$n d=t(n-1)$
$\Rightarrow t=\frac{n d}{(n-1)}$
Question 7
1 / -0

A laser beam is used for locating distant objects because it

A
is non directional

B
is non-coherent

C
is not absorbed

D
it is collimated

Solution

A laser beam is used for locating distant objects becauseit does not spread as it moves through the medium and has a very small angular spread i.e.it is collimated.
Question 8
1 / -0

The light gathering power of a camera lens depends on

A
its diameter only

B
ratio of focal length and diameter

C
product of focal length and diameter

D
wavelength of light used

Solution

Thelight-gathering powerof an optical telescope, also referred to aslightgrasp or aperture gain, is the ability of a telescope to collect a lot morelightthan the human eye.Essentially yes,light gathering abilityof alensis determined by its maximum aperture. Transmission rates of the materials used also has an effect but it is very small.The light-gathering power of a camera lens depends onratio of focal length and diameter.
Question 9
1 / -0

To get three images of a single object, one should have two plain mirrors at an angle of:

A
60⁰

B
90⁰

C
120⁰

D
30⁰

Solution

let angle =$90^{\circ},$
we get $n=\frac{360}{0}-1$
Here $\frac{360^{\circ}}{90^{\circ}}-1=4-1=3$
So we get 3 images at $90^{\circ}$
Question 10
1 / -0

A ray falls on a prism ABC (AB = BC) and travels as shown in figure. The least value of refractive index of material of the prism, should be:

A
1.5

B
^$\sqrt{2}$

C
1.33

D
^$\sqrt{3}$

Solution