Atoms — Physics STD 12 Science — Question

The wire wound resistor is also known as:

Two straight horizontal parallel wires are carrying the same current in the same direction, d is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires

(a) At a distance d/2  from any of the wires

(b) At a distance d/2  from any of the wires in the horizontal plane

(c) Anywhere on the circumference of a vertical circle of radius d and centre halfway between the wires

(d) At points halfway between the wires in the horizontal plane

A raindrop falls near the surface of the earth with almost uniform velocity because:

1. Its weight is negligible.
2. The force of surface tension balances its weight.
3. The force of viscosity of air balances its weight.
4. The drops are charged and atmospheric electric field balances its weight.

A coil of 100 turns carries a current of 5 mA and creates a magnetic flux of 10^–5 weber. the inductance is

(a) 0.2 mH

(b) 2.0 mH

(c) 0.02 mH

(d) None of these

The photoelectric threshold wavelength for potassium (work function being 2eV ) is

(a) 310 nm

(b) 620 nm

(c) 1200 nm

(d) 2100 nm

Yellow light is used in single slit diffraction experiment with slit width 0.6 mm. If yellow light is replaced by X-rays then the pattern will reveal

(a) That the central maxima is narrower	(b) No diffraction pattern
(c) More number of fringes	(d) Less number of fringes

In Boolean algebra, A + B = Y implies that:

In extrinsic semiconductors

(a) The conduction band and valence band overlap

(b) The gap between conduction band and valence band is more than 16 eV

(c) The gap between conduction band and valence band is near about 1 eV

(d) The gap between conduction band and valence band will be 100 eV and more