Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Light from a hydrogen discharge tube is incident on the cathode of a photoelectric cell the work function of the cathode surface is 4.2 eV. In order to reduce the photo-current to zero the voltage of the anode relative to the cathode must be made (a) – 4.2 V(b) – 9.4 V(c) – 17.8 V(d) +9.4 V

A hollow tube is carrying an electric current along its length distributed uniformly over its surface. The magnetic field:

1. Increases linearly from the axis to the surface.
2. Is constant inside the tube.
3. Is zero at the axis.
4. Is zero just outside the tube.

P-type semiconductor is formed when
A. As impurity is mixed in Si                                                                         B. Al impurity is mixed in Si
C. B impurity is mixed in Ge                                                                         D. P impurity is mixed in Ge(a) A and C(b) A and D(c) B and C(d) B and D

The decay constant λ  of the radioactive sample is the probability of decay of an atom in unit time, then(a) λ decreases as atoms become older(b) λ increases as the age of atoms increases(c) λ is independent of the age(d) Behaviour of λ with time depends on the nature of the activity

A thermoelectric refrigerator works on(a) Joule effect(b) Seeback effect(c) Peltier effect(d) Thermonic emission

Among the following one can act as the building blocks for the other gates is:

Susceptibility is positive and large for a:

If the direction of the initial velocity of a charged particle is neither along nor perpendicular to that of the magnetic field, then the orbit will be: