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

1 newton/coulomb is equivalent to

• 1 C/V

• 1 J

• 1 V/M

• 1 J/C

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

• $\frac{\mathrm{\nu }}{\mathrm{Br}}$

• Bvr²

• $\frac{\mathrm{B}}{\mathrm{r\nu }}$

45.

Number of extra electrons in a body of charge -80$\mathrm{\mu }$C, is

• 80 × 10¹⁵

• 80 × 10⁻¹⁵

• 5 × 10¹⁴

• 1.28 × 10⁻¹⁷

A radioactive substance containing N atoms emits n $\alpha$ - particles per second. Half-life of the substance is :

• $\frac{\mathrm{N}}{\mathrm{n}}$ sec

• $\frac{\mathrm{n}}{\mathrm{N}}$ sec

• $\frac{0.693\mathrm{n}}{\mathrm{N}}$ sec

• $\frac{0.693\mathrm{N}}{\mathrm{n}}$ 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 $\frac{3}{2}$ and $\frac{4}{3}$ respectively. The value of the critical angle will be :

• ${\sin }^{-1}\left(\frac{1}{2}\right)$

• ${\sin }^{-1}\left(\frac{9}{8}\right)$

• ${\sin }^{-1}\left(\frac{8}{9}\right)$

• ${\sin }^{-1}\left(\frac{5}{7}\right)$

In a radioactive decay,

           ₉₂U²³⁸ _{$\stackrel{\mathrm{\alpha }}{\to }$  X  $\stackrel{\mathrm{\alpha }}{\to }$  Z}Y^A

The values of Z and A

• 92 , 236

• 88 , 230

• 90 , 130

• 88 , 234

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