When accelerated electrons are direct against an anticathode in an X-ray tube, the radiation obtained has a continuous spectrum with a wavelength minimum,

$\lambda$_min = (1.24 x 10^-6/V) m, where V is the voltage used for accelerating the electrons. Calculate $\lambda$_min for V= 5 x 10⁴ volts.

(A) 1.25 Å

(B) 0.75 Å

(C)0.25 Å

(D) 1.00 Å

The wavelengths of two photons are 2000 Å and 4000 Å respectively. What is the ratio of their energies?

(1) 1/4

(2) 4

(3) 1/2

(4) 2

The ion that is isoelectronic with CO is-

(A) CN^-

(B) O₂⁺

(C) O₂^-

(D) N₂⁺

When the atoms of gold sheet are bombarded with a beam of $\alpha$ -particles, only a few a-particles get deflected where as most of them go straight undeflected. This is because

(A) The force of attraction on the $\alpha$-particles by the oppositely charged electron is not sufficient

(B) The nucleus occupies much smaller volume as compared to the volume of atom

(C) The force of repulsion on fast moving $\alpha$-particles is very small.

(D) The neutrons in the nucleus do not have any effect on $\alpha$-particles

The brackett series of spectral lines arise when an electron in an excited hydrogen atom jumps from an energy level

(1) n=5 to n=1

(2) n=5 to n=3

(3) n=5 to n=4

(4) n=5 to n=2

The ratio of the wavelengths of last lines of Balmer and Lyman series is-

(A) 4:1

(B) 27:5

(C) 3:1

(D) 9:4

Frequency ratio between violet (400nm) and red (750nm) radiations in the visible spectrum, is-

(1) 8/15

(2) 4/15

(3) 15/8

(4) None of these

Two isotopes of Boron are found in the nature with atomic weights 10.01(I) and 11.01(II). The atomic weight of natural Boron is 10.81. The percentage of (I) and (II) isotopes in it are respectively-

(A) 20 and 80

(B) 10 and 90

(C) 15 and 75

(D) 30 and 70

There are three energy levels in an atom. How many spectral lines are possible in its emission spectra?

1. One

2. Two

3. Three

4. Four

The increasing order of energy of electromagnetic radiation can be represented as: