Atoms — Physics STD 12 Science — Question

The figure here gives the electric field of an EM wave at a certain poiunt and a certain instrant. the wave is transporting energy in the negative z direction. what is tha direction of the magnetic field of the wave at that point and instant.

1 Curie is equal to

(a) 3  disintegrations/sec	(b) 3.7   disintegrations/sec
(c) 5 disintegrations/sec	(d) 3.7  disintegrations/sec

While tuning in a certain broadcast station with a receiver, we are actually

(a) Varying the local oscillator frequency

(b) Varying the frequency of the radio signal to be picked up

(c) Tuning the antenna

(d) None of these

When the accelerating voltage applied on the electrons increased beyond a critical value

(a) Only the intensity of the various wavelengths is increased

(b) Only the wavelength of characteristic relation is affected

(c) The spectrum of white radiation is unaffected

(d) The intensities of characteristic lines relative to the white spectrum are increased but there is no change in their wavelength

The radiant energy of the sun results from:

The potential difference applied to an X-ray tube is increased. As a result, in the emitted radiation:

The wavelength of X-rays is of the order of

(a) Centimetre

(b) Micron (10-6 m)

(c) Angstrom (10-10 m)

(d) Metre

A prism having an apex angle 4^o and refraction index 1.5 is located in front of a vertical plane mirror as shown in figure. Through what total angle is the ray deviated after reflection from the mirror

(a) 176o

(b) 4o

(c) 178o

(d) 2o

A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be

(a) 1600 A

(b) 20 A

(c) 4 A

(d) 1.5 A

The resistance of a discharge tube is

(a) Ohmic

(b) Non-ohmic

(c) Both (a) and (b)

(d) Zero