The core used in transformer and other electromagnetic instruments is laminated, the reason is
to increase the electric field
to increase the magnetic field
to reduce the loss of energy due to eddy currents
to decrease the resistance
In a galvanometer of 5 ohm resistance, a wire of 2 ohm resistance is used as a shunt. If the total current is 1 ampere, the fraction of current that will flow through the shunt is
1.2 A
0.7 A
0.5 A
0.3 A
An electron is moving with velocity v on a circular path of radius r in a transverse electric field B. The specific charge (e/m) of the electron is
Bvr
Bvr2
Number of extra electrons in a body of charge -80C, is
80 × 1015
80 × 10−15
5 × 1014
1.28 × 10−17
A radioactive substance containing N atoms emits n - particles per second. Half-life of the substance is :
sec
sec
sec
sec
If the temperature of a black body is doubled, the wavelength at which the spectral radiancy has its maximum, is
doubled
halved
quadrupled
unchanged
A light wave travels from glass to water. The refractive indices for glass and water are and respectively. The value of the critical angle will be :
The wavelength of light coming from a distant galaxy is found to be 0.5% greater than the wavelength of light coming from a stationary source. The galaxy is
coming towards earth with velocity of light
moving away from earth with velocity 1.5 x 106 m/sec
stationary with respect to earth
moving away from earth with velocity of light
B.
moving away from earth with velocity 1.5 x 106 m/sec
Wavelength displacement
------------- (1)
Suppose the wavelength coming from a source on the earth =
and the wavelength coming from galaxy =
= (1+0.5%)
= 1.005
or = 1.005
or =
or =
or = 1.005 - 1
or = 0.005
=
0.005 =
v = 0.005 × 3 × 108
= 1.5 × 106 m/s
Since,wavelength is increasing,therefore galaxy is moving away from the earth with a velocity of 1.5 × 106 m/s.