Identify the correct statement(s) among the following.
1. Electrical conductivity in an intrinsic semiconductor is due to electrons excited from the conduction band to valence band.
2. In germanium atom electrical conductivity is due to intrinsic charge carriers.
3. In doped atoms, the size of the dopant atom should be almost the same as that of the intrinsic crystal.
4. In n-type semiconductor, the donor atom becomes negatively charged.
Choose correct answer from the options given below:

If the work function of a target is 1.25 eV and the wavelength of incident radiation is 2460 \( \text{\AA} \), the stopping potential required to stop the emitted electrons is :
Given : \( h = 6.6 \times 10^{-34} \text{ Js} \)

The sensitivity of a potentiometer can be increased by:

Identify the wrong nuclear equation :

The formation of rainbow is an example of

When light travels from one medium to another medium of different refractive index, then the wave will have change in its :

Three concentric metallic spherical shells of radii \( R, 2R \), and \( 3R \) are given charges \( Q_1, Q_2 \) and \( Q_3 \), respectively. It is found that the surface charge densities on the outer surfaces of the shells are equal. Then, the ratio of the charges given to the shells \( Q_1 : Q_2 : Q_3 \) is:

Read the following passage carefully and answer the given questions.
The B-lymphocytes produce an army of proteins in response to pathogens. Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains. Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection. Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing. The use of drugs like anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy. Lymphoid organs are the organs where origin and/or maturation and proliferation of lymphocytes occur. The primary lymphoid organs are bone marrow and thymus. After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer's patches of small intestine and appendix. Heroin commonly called smack is chemically diacetylmorphine which is a white, odourless, bitter crystalline compound. This is obtained by acetylation of morphine, which is extracted from the latex of poppy plant Papaver somniferum.
Heroin, commonly called smack and chemically is -

A photo cathode is illuminated by a very small bright source placed 1 m away. When the same source of light is placed 0.5 m away, the number of electrons emitted by the photo cathode would become

In a large building, there are 20 bulbs of 40 W each, 5 bulbs of 100 W each, 5 fans of 80 W each, and 1 heater of 1 kW. The voltage supply is 220 V. The minimum capacity of the main fuse of the building should be

When the cells from malignant tumours start invading and damaging the normal tissues and reach distant sites through blood, the process is known as :

Arrange the following in increasing order of their basic strength
(I) \(C_6H_5NH_2\)
(II) \(C_2H_5NH_2\)
(III) \(NH_3\)

The current in a wire varies with time according to the relationship; I = (2 + 2 t) A, where t is time in seconds. The charge passing through a cross-section of the wire in the time interval between t = 0 s to t = 4 s is