Physics Test 128

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Physics Test 128

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Question 1
4 / -1

A planet of core density 3ρ and outer curst of density ρ has small tunnel in core. A small Particle of mass m is released from end A then time required to reach end B :

A

B

C

D

Solution

At some distance from centre inside core
Question 2
4 / -1

A small circular wire loop of radius a is located at the centre of a much larger circular wire loop of radius b as shown above (b> >a). Both loops are coaxial and coplanar. The larger loop carries a time (t) varying current I = I₀ cos ωt where I₀ and ω are constants. The large loop induces in the small loop an emf that is approximately equal to which of the following.

A

B

C

D

Solution

Magnetic flux passing through inner loop due to current in outer loop-
Question 3
4 / -1

A spring mass system is placed on a frictionless horizontal surface as shown in the figure. The spring is expanded by 1/10m and the blocks are given velocities as shown, then maximum extension of spring is :

A

B

C

D

Solution

As there is no loss of energy
Initial mechanical energy = Final mechanical energy
For initial Mechanical energy

= 25 + 25 = 50
For final Mechanical energy
When there is maximum extension relative velocity between block = 0
Question 4
4 / -1

An electromagnetic wave of frequency f = 7.3MHz passes from a vacuum into a dielectric medium with permittivityε = 9. Then,

A
Frequency of the wave will remains same but wavelength will become thrice

B
Frequency remains same but the Velocity and wavelength both will become 3 times of the original value

C
Velocity and frequency both will become 1/3 times of the original value

D
Frequency remains same but the Velocity and wavelength both will become 1/3 times of the original value

Solution

As permittivity is greater than the permittivity of free space so the refractive index of medium is

Wavelength of the electromagnetic wave in medium will be

Velocity of wave will be.
Question 5
4 / -1

A particle is projected from point A towards a building of height h as shown at an angle of 60 ° with horizontal. It strikes the roof of building at B at an angle of 30 ° with the horizontal. The speed of projection is

A
√gh

B
√2gh

C
√3gh

D
2√gh

Solution

Let u be the speed of projection and v be the speed at B
Question 6
4 / -1

Three identical bulbs each of resistance 2Ω are connected as shown. The maximum power that can be consumed by individual bulb is 32W, then the maximum power consumed by the combination is :

A
48 W

B
96 W

C
128 W

D
160 W

Solution

Resistance of B₁, B₂ and B₃ are same which is = 2Ω
As P ∝i² (when ‘R’ constant)
So, maximum power consumed by bulb B₃
Which is = 32 W
⇒i²R = 32
⇒i² . (2) = 32
⇒i = 4 Ampere
So, current passing through B₁ + B₂ = i/2 = 2
Total power consumed in circuit
P = (i/2)² (2) + (i/2)² (2) + i²(2)
= (2)² (2) + (2)² (2) + (4)² (2)
= 48W
Question 7
4 / -1

A carrier wave has power of 1675 kW. If the side band power of a modulated wave subjected to 60%. Then find the amplitude modulation level

A
301.5 kW

B
942 kW

C
1392 kW

D
1884 kW

Solution

As you know that, sideband power is, Where P_Cis power of carrier wave, P_Ss sideband power and ‘m’ is modulation rate,
Question 8
4 / -1

Two identical conducting spheres each having radius r are placed at large distance. lnitially charge on one sphere is q, while charge on another sphere is zero when they are connected by conducting wire as shown in figure then find total heat produced when switch S is closed :

A

B

C

D
zero

Solution

When sphere connected by wire, charge will flow from one sphere to another until potential of both sphere become same.
Or,
As both sphere is identical in dimension and material, charge will divide equally

Now, Initial potential energy of system
Question 9
4 / -1

Four wire A, B, C and D each of length l = 10 cm and each of area of cross section is 0.1 m² are connected in the given circuit. Then, the position of null point is

Given that resistivity

A
mid point of wire B or wire C when both the switches, S₁ and S₂ open.

B
only mid point of wire B when both the switches, S₁ and S₂ are open.

C
mid point of wire D when both the switches S₁ and S₂ are open.

D
3 cm from the left end of B when both the switches S₁ and S₂ are open.

Solution

When S₁ and S₂ both open and jockey has no deflection then let current in upper circuit is ” i”.

When jockey is touched, and there is no deflection then potential difference between ‘A’ and the point should be same in both path-

So, in lower circuit as S₂ is open
No current will flow in this circuit
⇒Potential difference between A and P
Will be = 2V

For this point ‘P’ should be half way in wire C.
Similarly when jockey touched on wire ‘B’, Null point will be obtained at middle point of wire B.
Question 10
4 / -1

The radius of curvature of spherical surface is 10 cm. The spherical surface separates two media of refractive indices μ₂ = 1.3 and μ₃ = 1.5 as shown in Figure. The medium of refractive index 1.3 extends upto 78 cm from the spherical surface. A luminous point object O is at the distance of 144 cm from the spherical surface in the medium of refractive index μ₁ = 1.1. The image formed by the spherical surface is at

A
900 cm from O

B
900 cm from A in medium μ₃

C
900/7 cm from O

D
900/7 cm from A in medium μ₃

Solution

Distance of object from the spherical surface