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
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
1V
C.
An AC supply gives 30Vrms 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
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