Nuclei — Physics STD 12 Science — Question

The temperature (T) dependence of resistivity (r) of a semiconductor is represented by

(a)

(b)

(c)

(d)

The angle of polarisation for any medium is 60^o, what will be critical angle for this

(a)

(b)

(c)

(d)

The value of red colour in colour code of carbon resistance :

The continuous X-rays spectrum produced by an X-ray machine at constant voltage has

(a) A maximum wavelength	(b) A minimum wavelength
(c) A single wavelength	(d) A minimum frequency

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region:

A wire of length 5 m and radius 1 mm has a resistance of 1 ohm. What length of the wire of the same material at the same temperature and of radius 2 mm will also have a resistance of 1 ohm

(a) 1.25 m

(b) 2.5 m

(c) 10 m

(d) 20 m

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 particle of charge +q and mass m moving under the influence of a uniform electric field   and a uniform magnetic field   follows trajectory from P to Q as shown in figure. The velocities at P and Q are v  and -2v  respectively. Which of the following statement(s) is/are correct

(a) E =

(b) Rate of work done by electric field at P is

(c) Rate of work done by both the fields at Q is zero

(d) a, b, c

Mosley measured the frequency (f) of the characteristic X-rays from many metals of different atomic number (Z) and represented his results by a relation known as Mosley's law. This law is (a, b are constants)

(a) f = a

(b) Z =

(c)

(d)

According to the electromagnetic wave theory, light consists of electric and magnetic fields which are_____________.