Minimum excitation potential of Bohr's first orbit in hydrogen atom is
3.6 V
10.2 V
13.6 V
3.4 V
A luminous object is placed at a distance of 30 cm from the convex lens of focal length 20 cm. On the other side of the lens, at what distance from the lens a convex mirror of radius of curvature 10 cm be placed in order to have an upright image of the object coincident with it
30 cm
60 cm
50 cm
12 cm
C.
50 cm
Using the formula
v = 60 cm
If the image is formed at the centre of curvature of the mirror, the coincidence is possible. Then the rays refracting through the lens will fall normally on the convex mirror and retrace their path of form the image at 0. Hence, the distance between lens and mirror will be
60 - 10 = 50 cm
A point source of light is placed 4 m below the surface of water of refractive index 5/3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut-off all light coming out of water is
6 m
3 m
4 m
2 m
Ionisation potential of hydrogen atom is 13.6 eV. Hydrogen atom on the ground state rarely excited by monochromatic radiation of photon 12.1 eV. The special line emitted by a hydrogen atom according to Bohr's theory will be
one
two
three
four
Two coherent light beams of intensities I and 41 are superposed. The maximum and minimum possible intensities in the resulting beam are
5I and I
5I and 3I
9I and I
9I and 3I
The half-life of radio isotope is 4 h. If initial mass of the isotope was 200 g, then mass remaining after 24 h will be
1.042 g
2.084 g
3.125 g
4.167 g
The work function for metals A, Band C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein's equation the metals which will emit photo, electrons for a radiation of wavelength 4100 Ao is/are
none
A only
A and B only
All the three metals