31.

A rectangular loop carrying a current i₁, is situated near a long straight carrying a straight current  i₂. The wire is parallel to one of the sides of  the loop as shown in the figure. Then the current loop will 

• move away from the wire

• move towards the wire

• remain stationary

• rotate about axis parallel to wire

The maximum distance upto which TV transmission from a TV of height h can be received is proportional to

• h^1/2

• h

• h³

• h²

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 10¹¹ per  m³ ?

• 2 MHz

• 10 MHz

• 12 MHz

• 18 MHz

Using mass (M), length (L), time (T ) and current (A) as fundamental quantities, the dimension of permeability is

• [ M^-1 L T^-2 A ]

• [ M L² T^-2 A^-1 ]

• [ M L T^-2A^-2 ]

• [ M L T^-1 A^-1 ]

A laser beam is used for carrying out surgery because it

• is highly monochromatic

• is highly coherent

• is highly directional

• can be sharply focused

A proton is about 1840 times heavier than an electron. When it is accelerated by a potential difference of 1 kV, its kinetic energy will be

• 1840 keV

• 1/1840 keV

• 1 keV

• 920 keV

To a germanium sample, traces of gallium are added as an impurity. The resultant  sample would behave like

• a conductor

• a p-type semiconductor

• an n-type semiconductor

• an insulator

A radioactive substance decays to 1/16^th of its initial activity in 40 days. The half-life of the radioactive substance expressed in days is

• 2.5

• 5

• 10

• 20

A neutron makes a head-on elastic collision with a stationary deuteron. The fractional energy loss of the neutron in the collision is

• 16/81

• 8/9

• 8/27

• 2/3

When a beam of light is used to determine the position of an object, the maximum accuracy is achieved if the light is

• polarised

• of longer wavelength

• of shorter wavelength

• of high intensity