11. Which of the following, when added as an impurity, into the silicon, produces n-type semiconductor ?

67. The hypermetropia is a ?

29. An achromatic combination of lenses is formed by joining ?

28. A lens is placed between a source of light and a wall. It forms images of area $A_1$ and $A_2$ on the wall for its two different positions. The area of the source of light is ?

2. If two mirrors are kept inclined at $60^◦$ to each other and a body is placed at the middle, then total number of images formed is ?

If the potential of a capacitor having capacity 6μF is increased from 10 V to 20 V, then increase in its energy will be ?

The formation of a dipole is due to two equal and dissimilar point charges placed at a ?

An electric dipole, consisting of two opposite charges of 2 × 10−6C each separated by a distance 3 cm is placed in an electric field of 2 × 105 N/C. Torque acting on the dipole is ?

There is an electric field E in X-direction. If the work done on moving a charge of 0.2C through a distance of 2 m along a line making an angle 60◦ with x-axis is 4 J, then what is the value of E ?

A charge ’ q ’ is placed at the centre of the line joining two equal charges ’ Q ’. The system of the three charges will be in equilibrium if ’ q ’ is equal to ?

If the force on a rocket moving with a velocity of 300 m/sec is 345 N, then the rate of combustion of the fuel, is