JEE Physics paper for practice

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JEE Physic Paper set 3

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A paramagnetic sample shows a net magnetisation of 8 Am^-1 when placed in an external magnetic field of 0.6 T at a temperature of 4K. When the same sample is placed in an external magnetic field of 0.2 T at a temperature of 16 K, the magnetisation will be

1 32/3 Am-1

2 2/3 Am-1

3 6 Am-1

4 2.4 Am-1

S is the surface of a lump of magnetic material.

1 Lines of B are not necessarily continuous across S.

2 Some lines of B must be discontinuous across S.

3 Lines of H are necessarily continuous across S.

4 Lines of H cannot all be continuous across S.

The primary origin(s) of magnetism lies in

1 Pauli exclusion principle.

2 polar nature of molecules.

3 intrinsic spin of electron.

4 None of these.

A long solenoid has 1000 turns per metre and carries a current of 1 A. It has a soft iron core of μ_r = 1000. The core is heated beyond the Curie temperature, T_c .

1 The H field in the solenoid is (nearly) unchanged but the B field decreases drastically.

2 The H and B fields in the solenoid are nearly unchanged.

3 The magnetisation in the core reverses direction.

4 The magnetisation in the core does not diminishes.

. Essential difference between electrostatic shielding by a conducting shell and magne-tostatic shielding is due to

1 electrostatic field lines cannot end on ’ charges and conductors do not have free charges.

2 lines of B can also end but conductors cannot end them.

3 lines of B cannot end. on any material and perfect shielding is not possible.

4 shells of high permeability materials cannot be used to divert lines of B from the interior region.

Let the magnetic field on earth be modelled by that of a point magnetic dipole at the centre of earth. The angle of dip at a point on the geographical equator

1 is always zero.

2 can be zero at specific points.

3 cannot be positive or negative.

4 is not bounded.

A 25 cm long solenoid has radius 2 cm and 500 total number of turns. It carries a current of 15 A. If it is equivalent to a magnet of the same size and magnetisation M¯, then |M| is

1 3 π Am-1

2 30000 π Am-1

3 300 Am-1

4 30000 Am-1

Three needles N₁ N₂ and N₃ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet, when brought close to them, will
(?) attract N₁ strongly, but repel N₂ and N₃ weakly.

1 attract all three of them.

2 attract N1 strongly, but repel N2 and N3 weakly.

3 attract N1 and N2 strongly but repel N3.

4 attract N1 strongly, N2 weakly and repel N3 weakly.

The best material for the ore of a transformer is

1 stainless steel

2 mild steel

3 hard steel

4 soft iron

Electromagnetic waves travelling in a medium having relative permeability μ_r = 1.3 and relative permittivity E_r = 2.14. The speed of electromagnetic waves in medium must be

1 1.8 × 108 ms-1

2 1.8 × 104ms1

3 1.8 × 106ms1

4 1.8 × 10² ms-1

1.8 × 10² ms^-1The condition under which a microwave over heats up a food item containing water molecules most efficiently is

1 The frequency of the microwaves must match the resonant frequency of the water molecules.

2 The frequency of the microwaves has no relation with natural frequency of the water molecules.

3 Microwaves are heat waves, so always produce heating.

4 Infrared waves produce heating in a microwave oven.

The correct option, if speeds of gamma rays, X-rays and microwave are V_g, V_x and V_m respectively will be.

1 Vg > Vx > Vm

2 Vg < Vx < Vm

3 Vg > Vx > Vm

4 Vg = Vx = Vm

Waves in decreasing order of their wavelength are

1 X-rays, infrared rays, visible rays, radio waves

2 radio waves, visible rays, infrared rays, X-rays.

3 radio waves, infrared rays, visible rays, X-rays.

4 radio waves, ultraviolet rays, visible rays, X-rays.

The electric field associated with an e.m wave in vacuum is given by E? =40 cos (kz – 6 × 10⁸) i? , where E, Z and t are in volt/m, metre and seconds respectively. The value of wave vector K is

1 2 m-1

2 0.5 m-1

3 6 m-1

4 3 m-1

The oscillating magnetic field in a plane electromagnetic wave is given as B_y = (8 × 10^-6) sin [2 × 10¹¹t+ 300πx] T, wavelength of the em wave is

1 0.80 cm

2 1 × 103m

3 2 × 10-2cm

4 0.67 cm

charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. The frequency of electromagnetic waves produced by the oscillator is

1 106 Hz

2 107 Hz

3 108 Hz

4 109 Hz

Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 minutes is

1 36 × 10-5 kg m/s.

2 36 × 10-4 kg m/s.

3 108 × 104 kgm/s.

4 1.08 × 107 kg m/s.

An electromagnetic wave travelling along z-axis is given as-E=E0 cos (kz – cot). Choose the incorrect option from the following;

1 The associated magnetic field is given as B = 1ck^ × E = 1ω(k^ × E)

2 he electromagnetic field can be written in terms of the associated magnetic field as E = c(B × k^)

3 k^.E = 0, k^.B =0.

4 k^ × E = 0, kk^ × B = 0.

A charged particle oscillates about its mean equilibrium position with a frequency of 10⁹ Hz. For producing electromagnetic waves which one is not true?

1 They will have frequency of 109 Hz.

2 They will have frequency of 109 Hz.

3 They will have a wavelength of 0.3 m.

4 They fall in the region of radio waves.