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

Carbon, silicon and germanium have four valence electrons each. At room temperature the appropriate statement is:

The current in a simple series circuit is 5.0 amp. When an additional resistance of 2.0 ohms is inserted, the current drops to 4.0 amp. The original resistance of the circuit in ohms was(a) 1.25(b) 8(c) 10       (d) 20

Work function of a metal is 2.1 eV. Which of the waves of the following wavelengths will be able to emit photoelectrons from its surface(a) 4000 Å, 7500 Å(b) 5500 Å, 6000 Å (c) 4000 Å, 6000 Å(d) None of these

When air in a capacitor is replaced by a medium of dielectric constant K, the capacity:

The reciprocal of resistance is (a) Conductance(b) Resistivity(c) Voltage(d) None of the above

The distance between the body centred atom and a corner atom in sodium (a = 4.225 Å) is(a) 3.66 Å(b) 3.17 Å(c) 2.99 Å  (d) 2.54 Å

Consider a moving charged particle in a region of magnetic field. Which of the following statements are correct?

1. If v is parallel to B, then path of particle is spiral.
2. If v is perpendicular to B, then path of particle is a circle.
3. If v has a component along B, then path of particle is helical.
4. If v is along B, then path of particle is a circle.

When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor: