Electromagnetic Waves — Physics STD 12 Science — Question

The dielectric constant k of an insulator cannot be

(a) 3

(b) 6

(c) 8

(d) ∞

Which of the following electromagnetic waves has the longest wavelength ?

The  electric charge in uniform motion produces

(a) An electric field only	(b) A magnetic field only
(c) Both electric and magnetic field	(d) Neither electric nor magnetic field

An electron in the n = 1 orbit of hydrogen atom is bound by 13.6 eV. If a hydrogen atom is in the n = 3 state, how much energy is required to ionize it

(a) 13.6 eV

(b) 4.53 eV

(c) 3.4 eV

(d) 1.51 eV

An electron of mass  initially at rest moves through a certain distance in a uniform electric field in time . A proton of mass  also initially at rest takes time  to move through an equal distance in this uniform electric field. Neglecting the effect of gravity, the ratio of  is nearly equal to

(a) 1

(b)

(c)

(d) 1836

There are two conductors X and Y carrying a current I and moving in the same direction. p and q are two electron beams also moving in the same direction. Will there be attraction or repulsion between the 2 conductors and between the two electron beams separately?

If the potential difference applied to the tube is doubled and the separation between the filament and the target is also doubled, the cutoff wavelength:

1. Will remain unchanged.
2. Will be doubled.
3. Will be halved.
4. Will become four times the original.

The pressure in a liquid at two points in the same horizontal plane are equal. Consider an elevator accelerating upward and a car accelerating on a horizontal road. The above statement is correct in:

1. The car only.
2. The elevator only.
3. Both of them.
4. Neither of them.

Assertion  :   Leclanche cell is used, when constant supply of electric current is not required.  

Reason     : The e.m.f. of a Leclanche cell falls, if it is used continuously.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

The mass number of He is 4 and that for sulphur is 32. The radius of sulphur nucleus is larger than that of helium, by times

(a)

(b) 4

(c) 2

(d) 8