## In an X-ray tube , electrons emitted from a filament (cathode) carrying current I hit a target (anode) ….

Q: In an X-ray tube , electrons emitted from a filament (cathode) carrying current I hit a target (anode) at a distance d from the cathode . The target is kept at a potential V higher than the cathode resulting in emission of continuous and characteristics X-rays . If the filament current I is decreased to I/2 , the potential difference V is increased to 2V ,and the separation distance d is reduced to d/2 then

(a) the cut-off wavelength will reduce to half and the wavelength of the characteristics X-rays will remain the same

(b) the cut-off wavelength as well as the wavelength of the characteristics X-rays will remain the same

(c) the cut-off wavelength will reduce to half and the intensities of all the X-rays will decrease

(d) the cut-off wavelength will become two times larger and the intensity of all the X-ray will decrease

Click to See Solution :
Ans: (a,c)

Sol: $\lambda \propto \frac{1}{V}$

So when V double , then cut-off wavelength becomes half . Characteristics does not depend on voltage . When I is halved then intensity will decrease

## Heavy stable nuclei have more neutrons than protons. This is because of the fact that

Q: Heavy stable nuclei have more neutrons than protons. This is because of the fact that

(a) neutrons are heavier than protons

(b) electrostatic force between protons are repulsive

(c) neutrons decay into protons through beta decay

(d) nuclear forces between neutrons are weaker than that between protons

Ans: (b)

## The gravitational force between a H-atom and another particle of mass m will be given by Newton’s law F= G (M.m)/r^2 , where r is in km and

Q: The gravitational force between a H-atom and another particle of mass m will be given by Newton’s law F = G (M.m)/r2 , where r is in km and

(a) M = mproton + melectron

(b) M = mproton + melectron -B/C2 (B = 13.6 eV)

(c) M is not relate to the mass of the hydrogen atom.

(d) M = mproton + melectron -|V|/C2 ; (|V| = magnitude of the potential energy of electron in the H-atom.

Ans: (b)

## Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half life of 1 yr. After 1 yr,

Q: Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half life of 1 yr. After 1 yr,

(a) all the containers will have 5000 atoms of the material

(b) all the containers will contain the same number of atoms of the material but that number will only be approximately 5000

(c) the container will in general have different numbers of the atoms of the material but their average will be close to 5000

(d) none of the containers can have more than 5000 atoms

Ans: (c)