Physics Test 175

Result

Physics Test 175

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Question 1
4 / -1

A wooden stick of length 3l is rotated about an end with constant angular velocity w in a uniform magnetic field B perpendicular to the plane of motion. If the upper one third of its length in coated with copper, the potential difference across the copper coating of the stick is

A

B

C

D

Solution

When the rod rotates, there will be an induced current in the rod. The given situation can be treated as if a rod 'A' of length '3ℓ' rotating in the clockwise direction, while an other rod 'B. of length '2ℓ' rotating in the anticlockwise direction with same angular speed 'ω'.
Question 2
4 / -1

The resistance of each straight section is r. Find the equivalent resistance between A and B.

A
3 r

B
3.5 r

C
4 r

D
4.5 r

Solution

From symmetry, the current distribution in branches LP, MP, NP and OP are as shown in figure 1. Therefore junction at P can be broken as shown in figure 2
Question 3
4 / -1

PQ is an infinite current carrying conductor. AB and CD are smooth conducting rods on which a conductor EF moves with constant velocity V as shown. The force needed to maintain constant speed of EF is.

A

B

C

D

Solution
Question 4
4 / -1

When a galvanometer is shunted with a 4 Ω resistance, the deflection is reduced to one-fifth. If the galvanometer is further shunted with a 2 Ω wire, the further reduction in the deflection will be (the main current remains the same).

A
(8/13) of the deflection when shunted with 4 Ω only

B
(5/14) of the deflection when shunted with 4Ω only

C
(3/4) of the deflection when shunted with 4Ω only

D
(3/13) of the deflection when shunted with 4Ω only

Solution

Hence further reduction in deflection = 8/13 of the deflection when shunted with 4Ω only.
Question 5
4 / -1

Figure shows a system of three concentric metal shells A, B and C with radii a, 2a and 3a respectively. Shell B is earthed and shell C is given a charge Q. Now if shell C is connected to shell A, then the final charge on the shell B, is equal to :

A

B

C

D

Solution
Question 6
4 / -1

Two small pith balls, each carrying a charge q are attached to the ends of a light rod of length d, which is suspended from the ceiling by a thin torsion free fiber as shown in figure. There is a uniform magnetic field B pointing straight down, in the cylindrical region of radius R around the fiber. The system is initially at rest. If the magnetic field is turned off. Which of the following happen to the system -

A
It rotate with an angular momentum qBR²

B
It does not move at all

C
It rotate with an angular momentum qBR² / 2

D
None of the above

Solution
Question 7
4 / -1

In a practical wheat stone bridge circuit as shown, when one more resistance of 100 ? is connected in parallel with unknown resistance ' x ', then ratio l₁/ l₂ becomes '2'. l₁ is balance length. AB is a uniform wire. Then value of ' x ' must be :

A
50 ?

B
100 ?

C
200 ?

D
400 ?

Solution
Question 8
4 / -1

The work function of a metal is 1 eV. When the surface of this metal is illuminated with light of wavelength 64000 Å, then the maximum kinetic energy of emitted photoelectron will be

A
31 × 19^–19 J

B
3.1 × 10^–19 J

C
0.15 × 10^–19 J

D
1.5 × 10^–19 J

Solution

ϕ₀ = 1 w; hv = energy of incident photon.

x = 64000 Å; c = 3 ×10⁸ms^-1; h = 6.6 x 10^-34 Js.

The K_max = hc/λ - ϕ₀, 1 ev. = 1.6 x 10^-19 Joule.
Question 9
4 / -1

If K₁ and K₂ are maximum kinetic energies of photoelectrons emitted when lights of wavelength λ₁and λ₂ respectively incident on a metallic surface and λ₁ = 3λ₂ then

A
K₁ > (K₂ / 3)

B
K₁ < (K₂ / 3)

C
K₁ = 2K₂

D
K₂ = 2K₁

Solution
Question 10
4 / -1

A

B

C

D
none of these

Solution