Electric Charges and Fields — Physics STD 12 Science — Question

Which of the following is false for electric lines of force ?

It is desired to photograph the image of an object placed at a distance of 3m from the plane mirror. The camera which is at a distance of 4.5 m  from the mirror should be focussed for a distance of

(a) 3m

(b) 4.5m

(c) 6m

(d) 7.5 m

A magnetic dipole of length 10cm has pole strength of 20Am. Find the magnetic moment of the dipole.

The resistance of a 5 cm long wire is 10 W.  It is uniformly stretched so that its length becomes 20 cm.  The resistance of the wire is

(a) 160 W

(b) 80 W

(c) 40 W

(d) 20 W

The maximum kinetic energy of a photo electron emitted from a metal is 1.8 eV . The value of stopping potential (cut-off voltage) will be :

Which of the following figure represents the variation of particle momentum and the associated de-Broglie wavelength

(a)

(b)

(c)

(d)

Consider a simple circuit shown in Fig. stands for a variable resistance R'. R' can vary from R₀ to infinity. r is internal resistance of the battery (r < < R < < R₀).

In a hydrogen discharge tube it is observed that through a given cross-section 3.13   electrons are moving from right to left and 3.12  protons are moving from left to right. What is the electric current in the discharge tube and what is its direction

(a) 1 mA towards right	(b) 1mA towards left
(c) 2mA towards left	(d) 2mA towards right

What will be the resultant magnetic field at origin due to four infinite length wires. If each wire produces magnetic field 'B' at origin

(a) 4 B

(b)

(c) 2

(d) Zero