Physics Test

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Physics Test - 9

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Question 1
1 / -0

Total internal reflection takes place

A
when a ray moves from denser to rarer medium and incident angle is greater than critical angle

B
when a ray moves from rarer to denser medium and incident angle is less than critical angle

C
when a ray moves from rarer to denser medium and incident angle is equal to critical angle

D
None of the above

Solution

when a ray moves from denser to rarer medium and incident angle is greater than critical angle
Question 2
1 / -0

The dimensional formula of couple

A
ML²T^-2

B
MLT^-1

C
ML^-1T^-1

D
M¹L¹T^-2

Solution

When two equal yet opposite forces act on a body they said to be forming a couple. The dimensional formula of couple ML²T^-2

Moment of a couple is calculated by multiplying the size of one of the force (F) by the perpendicular distance between the two forces.

Thus the units are that of Nm and dimensions are [(M1LT−2)(L)]=[M1L2T−2]
Question 3
1 / -0

The escape velocity for Earth is v_e. The escape velocity for a planet whose radius is four times and density is nine times that of Earth is

A
12v_e

B
18v_e

C
36v_e

D
48v_e

Solution

The relation between the escape velocity and the radius is given as $v_{e}=K r \sqrt{\rho}$
If the radius of the planet becomes four times and the density nine times then the escape velocity becomes
$v_{e 2}=36 v_{e}$
Question 4
1 / -0

In electromagnetic induction, the induced charge does not depend on –

A
Change in flux

B
time of change of magnetic flux

C
Resistance of Coil

D
None of the above

Solution

Induced charge does not depend upon time of change of magnetic flux, as Induced charge Q = n∆T∅R
Question 5
1 / -0

A bar magnet used in a vibration magnetometer is heated, so as to reduce its magnetic moment by 36%. The time period of the magnet (neglecting the changes in the dimension of the magnet) :

A
increases by 36%

B
decreases by 36%

C
increases by 25%

D
decreases by 25%

Solution

Time period, $T=2 \pi \sqrt{\frac{I}{M B_{H}}}$
$T \propto \frac{1}{\sqrt{M}}$
or $\frac{T_{1}}{T_{2}}=\sqrt{\frac{M_{2}}{M_{1}}}$
If $M_{1}=100$ then, $M_{2}=(100-36)=64$
So, $\frac{T_{1}}{T_{2}}=\sqrt{\frac{64}{100}}=\frac{8}{10}$
$T_{2}=\frac{10}{8} T_{1}=1.25 T_{1}$
So, \% increase in time period $=25 \%$
Question 6
1 / -0

A vertical spring with force constant 'k' is fixed on a table. A ball of mass 'm' at a height 'h' above the free upper end of the spring falls vertically on the spring, so that the spring is compressed by a distance 'd'. The net work done in the process is

A
$m g (h + d) + \frac{1}{2} k d^{2}$

B
$m g (h + d) - \frac{1}{2} k d^{2}$

C
$m g (h - d) - \frac{1}{2} k d^{2}$

D
$m g (h - d) + \frac{1}{2} k d^{2}$

Solution

When a mass falls on a spring from a height $h$
the work done by the loss of potential energy
of the mass is stored as the potential energy
of the spring.
One can write $m g(h+d)=\frac{1}{2} k d^{2}$
The two energies are equal.
If work done is initial P.E. - final P.E., it is zero.
Work done is totally converted (assuming
there is no loss. The work done in
compression or expansion is always positive
as it is $\propto x^{2}$. The
answer expected is
$m g(h+d)-\frac{1}{2} k d^{2} \quad o r, \quad \frac{1}{2} k d^{2}-m g(h+d)$
as seen from options, but it is not justified.
Question could have been more specific like
work done by oscillation.
Question 7
1 / -0

______________ is a thermodynamic process in which heat is not transferred into and out of a system or is typically obtained with strong insulating materials around the entire system.

A
isothermal process

B
adiabatic process

C
Thermal process

D
$β n$

Solution

An adiabatic process is a thermodynamic process in which heat transfer does not occur in a system or is usually achieved with a strongly insulating material around the entire system or by completing this process so quickly that there is not a significant time Heat transfer to take place.

A system that expands under adiabatic conditions performs positive work, so the internal energy decreases, and a system that contracts under adiabatic conditions acts negatively, so the internal energy increases.
Question 8
1 / -0

Which of the following quantities is used to determine the strength of the Earth's magnetic field at a point on the Earth's surface?
(I) magnetic damping
(II) Dip

A
Both I and II

B
Neither I nor II

C
only I

D
only II

Solution

Both, Because, dip to the angle L/w the horizontal and the magnetic field of the earth and declination is the angle L/w true north and magnetic north.
Question 9
1 / -0

A magnet makes 30 oscillations/min in Earth's magnetic field. If the magnetic field is doubled, the period of oscillation of magnet is

A
√2 s

B
2s

C
$12 s$

D
$12 s$

Solution

Time period of oscillation $T=2 \pi \sqrt{\frac{I}{M B_{H}}}$
$\therefore \frac{T_{2}^{2}}{T_{1}^{2}}=\frac{B_{1}}{B_{2}}$
$\frac{T_{2}^{2}}{(2)^{2}}=\frac{B}{2 B}$
$T_{2}^{2}=\frac{4}{2}$
$T_{2}=\sqrt{2} s$
Question 10
1 / -0

Which of the following is the most elastic?

A
Rubber

B
Glass

C
Steel

D
Plastic

Solution

In common reference,

Elasticity is the ability of a material to regain its own original shape after being stretched according to which, rubber is the most elastic substance.

But when we define elasticity in physics it is the ratio of stress to strain. It means that the shape which has more resistance to change is more elastic.

Hence, as per physics steel is the most elastic material.

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Physics Test - 9

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Physics Test - 9

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Question 1

when a ray moves from denser to rarer medium and incident angle is greater than critical angle

when a ray moves from rarer to denser medium and incident angle is less than critical angle

when a ray moves from rarer to denser medium and incident angle is equal to critical angle

None of the above

Solution

Question 2

ML2T-2

MLT-1

ML-1T-1

M1L1T-2

Solution

Question 3

12ve

18ve

36ve

48ve

Solution

Question 4

Change in flux

time of change of magnetic flux

Resistance of Coil

None of the above

Solution

Question 5

increases by 36%

decreases by 36%

increases by 25%

decreases by 25%

Solution

Question 6

mgh+d+12kd2

mgh+d-12kd2

mgh-d-12kd2

mgh-d+12kd2

Solution

Question 7

isothermal process

adiabatic process

Thermal process

βn

Solution

Question 8

Both I and II

Neither I nor II

only I

only II

Solution

Question 9

√2 s

2s

12s

12s

Solution

Question 10

Rubber

Glass

Steel

Plastic

Solution

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ML²T^-2

MLT^-1

ML^-1T^-1

M¹L¹T^-2

12v_e

18v_e

36v_e

48v_e

$m g (h + d) + \frac{1}{2} k d^{2}$

$m g (h + d) - \frac{1}{2} k d^{2}$

$m g (h - d) - \frac{1}{2} k d^{2}$

$m g (h - d) + \frac{1}{2} k d^{2}$

$β n$

$12 s$

$12 s$