Electric Charges and Fields — Physics STD 12 Science — Question

A moving coil galvanometer can be converted into voltmeter by:

The work function of a metal is 4.2 eV, its threshold wavelength will be(a) 4000 Å(b) 3500 Å(c) 2955 Å(d) 2500 Å

The capacitance of a parallel plate condenser does not depend on(a) Area of the plates(b) Medium between the plates(c) Distance between the plates(d) Metal of the plates

The spectral series of the hydrogen spectrum that lies in the ultraviolet region is the(a) Balmer series(b) Pfund series(c) Paschen series(d) Lyman series

The wavelength of X-rays is(a) 2000 Å(b) 2 Å(c) 1 mm(d) 1 cm

A wire is placed parallel to the lines of force in a magnetic field and a current flows in the wire. Then:

Assertion  :   Silicon is preferred over germanium for making semiconductor devices.
Reason      : The energy gap for germanium is more than the energy gap of silicon.(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.(c) If assertion is true but reason is false.(d) If the assertion and reason both are false.

A long straight horizontal cable carries a current of 2.5 A in the direction 10° south of west to 10° north of east. The magnetic meridian of the place happens to be 10° west of the geographic meridian. The earth’s magnetic field at the location is 0.33 Gauss, and the angle of dip is zero. Locate the line of neutral points. (Ignore the thickness of the cable).

Materials which allow only larger currents to flow through them are: