Physics Test

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Physics Test - 7

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Weekly Quiz Competition

Question 1
3 / -1

Whenever the magnetic flux linked with a coil changes, an induced e.m.f. is produced in the circuit. The e.m.f. lasts

A
for a short time

B
for a long time

C
for ever

D
so long as the change in flux takes place

Solution

It's a fact. Faraday's law says the induced emf in a coil is equal to the rate of change of magnetic flux through it. If the magnetic flux doesn't change then emf is zero.
Hence option D is the correct answer.
Question 2
3 / -1

Two equal masses hang on either side of a pulley at the same height from the ground. The mass on the right is given a horizontal speed, after some time.

A
The mass on the left will be nearer to ground

B
The mass on the right will be nearer to ground

C
Both the masses will be at equal distance from the ground.

D
Nothing can be said regarding their positions.

Solution

Now downward force on the right block is more.
[as the mass on the right moves with a horizontal velocity, the left mass will lift up.]
Hence option B is the correct answer.
Question 3
3 / -1

The number of turns in an air core solenoid of length 25 cm and radius 4 cm is 100. Its self inductance will be

A
5×10⁻⁴H

B
2.5×10⁻⁴H

C
5.4×10⁻³H

D
2.5×10⁻³H

Solution
Question 4
3 / -1

A pole of strength m_p is produced when a magnetic material of cross-sectional area A is placed in a magnetic field of strength H. The total magnetic flux will be

A
μ₀(AH+m_p)

B
μ₀AH

C
μ₀mp

D
μ₀[mpAH+A]

Solution
Question 5
3 / -1

In the circuit diagram shown below :

A
The effective capacitance between A and C 3/2 μF

B
The effective capacitance between A and C is 5/2μF

C
The potential difference between A and B in steady state is 75/2 volt

D
None of these

Solution

Hence option B is correct answer.
Question 6
3 / -1

In a series LR circuit, the voltage drop across the inductor is 8 volt and across the resistor is 6 volt. The voltage applied and the power factor of the circuit respectively are

A
14 V, 0.8

B
10 V, 0.8

C
10 V, 0.6

D
14 V, 0.6

Solution

The phase vectors of a resistor and an inductor make an angle of 90 degree with each other. Hence the net voltage will be obtained by taking the vector sum:

The power factor defined as the ratio of true power to apparent power will be given by V₁/V since the current flowing through the inductor and resistor is the same. Power factor = 6/10 = 0.6

Hence option C is the correct answer.
Question 7
3 / -1

A field of strength 5 × 10⁴ ampere turns / meter acts at right angles to the coil of 50 turns of area 10^-2 m² . The coil is removed from the field in . Then the induced e.m.f. in the coil is :

A
0.1 V

B
0.2 V

C
1.96 V

D
0.98 V

Solution
Question 8
3 / -1

A particle starts moving with initial velocity 3 m/s along x-axis from origin. Its acceleration is varying with x in parabolic nature as shown in figure. At x=√3 m tangent to the graph makes an angle 60∘ with positive x-axis as shown in diagram. Then at x =√3

A
$v = \sqrt{(\sqrt{3} + 9) m / s}$

B
v =√12 m/s

C
a= 3m/s²

D
None of these

Solution

Hence option A is the correct answer.
Question 9
3 / -1

The ratio of primary voltage to secondary voltage in a transformer is ‘n’. The ratio of the primary current to secondary current in the transformer is :

A
n

B
1/n

C
n²

D
1/n²

Solution
Question 10
3 / -1

A block of mass m is connected with another block of mass 2m by a light spring. 2m is connected with a hanging mass 3m by an inextensible light string. At the time of release of block 3m?

A
Tension in the string is 6/5mg.

B
Acceleration of m is zero.

C
Acceleration of 2m is 3g/5.

D
All of the above

Solution

Hence option D is the correct answer.
Question 11
3 / -1

The gravitational field in a region is given by $\vec{E}=(\hat{3} i-\hat{4} j) N k g^{-1}$ Find out the work done (in joule) in displacing a particle by $1 \mathrm{m}$ along the line $4 y=3 x+9$

A
1

B
0

C
3

D
6

Solution
Question 12
3 / -1

Two bar magnets are placed on a piece of cork which floats on water. The magnets are so placed that their axis are mutually perpendicular. Then the corkTwo bar magnets are placed on a piece of cork which floats on water. The magnets are so placed that their axis are mutually perpendicular. Then the cork

A
rotates

B
moves a side

C
oscillates

D
neither rotates nor oscillates

Solution

The cork will neither rotate nor oscillates as there will not be any interaction between the magnetic field lines of both the magnets on the cork.

Hence option D is the correct answer.
Question 13
3 / -1

Two coils of inductances L₁ and L₂ are linked such that their mutual inductance is M. Then M=

A
L₁+L₂

B
1/2(L₁+L₂)

C
(L₁±L₂)

D
√(L₁L₂)

Solution

Let us first consider a case when the total flux associated with one coil links with the other, i.e. a case of maximum flux linkage. Consider two coils placed adjacent to each other. Thus $M_{12}=\frac{N_{2} \phi_{B_{2}}}{i_{1}}$ and $M_{21}=\frac{N_{1} \phi_{B_{1}}}{i_{2}}$
and $L_{1}=\frac{N_{1} \phi_{B_{1}}}{i_{1}}$ and $L_{2}=\frac{N_{2} \phi_{B_{2}}}{i_{2}}$
If all the flux of coil 2 links coil i and vice versa, then $\phi_{B_{2}}=\phi_{B_{1}}$ As $M_{12}=M_{21}=M$
Thus we get $M_{12} M_{21}=M^{2}=\frac{N_{1} N_{2} \phi_{B_{1}} \phi_{B_{2}}}{i_{1} i_{2}}=L_{1} L_{2}$
or $M=\sqrt{L_{1} L_{2}}($ assuming that there is no flux leakage) Mutual inductance is inductance of emf in a coil due to change in current in another case for two coils which are mutually coupled has mutual inductance in $=\sqrt{L_{1} L_{2}}$ This is a general result assuming that there is no flux leakage.
Hence option D is the correct answer.
Question 14
3 / -1

The instantaneous potential difference between points A and B is (Phase angle is 37⁰)

A

B

C
10sin(50πt)

D
10cos(50πt)

Solution
Question 15
3 / -1

In a parallel plate capacitor the separation between the plates is 3mm with air between them. Now a 1mm thick layer of a material of dielectric to the original value the separation between the plates must be made

A
1.5 mm

B
2.5 mm

C
3.5 mm

D
4.5 mm

Solution