41.

 The capacity of a parallel plate capacitor with no dielectric substance but with a separation of 0.4 cm is 2µF. The separation is reduced to half and it is filled with a dielectric substance of value of 2.8. The final capacity of capacitor is

• 15.6μF

• 11.2μF

• 19μF

• 22.4μF

X-rays are

• electromagnetic radiation

• stream of electron

• stream of proton

• stream of uncharged particle

The plates of a parallel plate capacitor of capacity of 50 µF are charged by a battery to a potential of 100 volt. The battery remains connected the plates are separated from each other so that the distance between them is doubled. Then, the energy spent by battery in doing so, will be

• $12.5\times {10}^{-2}\mathrm{J}$

• $35\times {10}^{-2}\mathrm{J}$

• 42.5×10^-2J

• 25×10^-2J

Two small magnets each of magnetic moment 10 Am² are placed in end on position 0.1 m apart from their centres. The force acting between them is

• 0.6N

• 0.06N

• 0.06×10⁷N

• 0.6×10⁷N

 Magnetic field of a short magnet at a distance lm on axial line is 1 oersted at a distance 2 m on the same line the intensity in oersted is

• 0.75

• 0.125

• 0.25

• 0.5

The ratio of magnetic moments of two short magnets which give null deflection in tan B position at 12 cm and 18 cm from the centre of a deflection magnetometer is

• 4:9

• 27:8

• 2:3

• 8:27

If the flux associated with a coil varies at the rate of 1wb/min the induced emf is

• zero

• 6oV

• $\frac{1}{60}\mathrm{V}$

• 1V

An AC supply gives 30V_rms which is fed on a pure resistance of 10 ohm. the power dissipated in this is

• 90watt

• 45watt

• 90.2watt

• 180watt

The distance between the poles of horse shoe magnet is 10 cm and its pole strength is 10⁴ A. The magnetic field induction at point P mid-way between the poles is

• $8\times {10}^{-9} \mathrm{tesla}$

• 4×10^-19 tesla

• 2×10^-9 tesla

• zero

Light of wavelength 6000 A⁰ is reflected at nearly normal incidence from a soap film of refractive index 1.4. The least thickness of the film that will appear black is

• 200 A⁰

• 2000 A⁰

• 1000 A⁰

• Infinity