51.

The minimum energy to ionize an atom is the energy required to

• add one electron to the atom

• excite the atom from its ground state to its excited state

• remove one outer most electron from the atom

• remove one inner most electron from the atom

The distance between two point objects P and Q is 32 cm. A convex lens of focal length 15 cm is placed between them, so that the images of both the objects are formed at the same place. The distance of P from the lens could be

• 20 cm

• 12 cm

• 18 cm

• 28 cm

To get an output Y =1 from circuit of figure, the input must be

• A = 0, B = 1, C = 0

• A = 0, B = 0, C = 1

• A = 1, B = 0, C = 0

• A = 1, B = 0, C = 1

In hydrogen atom, the electron in a given orbit has total energy -1.5 eV. The potential energy is

• 1.5 eV

• - 1.5 eV

• 3.0 eV

• - 3.0 eV

The radii of curvature of the two surfaces of a lens are 20 cm and 30 cm and the repeative index of the material of the lens is 1.5. If the lens is concave-convex, then the focal length of the lens is

• 24 cm

• 10 cm

• 15 cm

• 120 cm

In a transistor circuit, the base current changes from 30 µA to 90 µA. If the current gain of the transistor is 30%, the change in the collector current is

• 4 mA

• 2 mA

• 3.5 mA

• 1.8 mA

In a full wave rectifier, input AC current has a frequency v. The output frequency of current is

• $\frac{\mathrm{v}}{2}$

• v

• 2 v

• None of these

When the distance between slits of Young's double slit experiment is reduced to half then the fringe middle will become

• constant

• four times

• two times

• half

Light of wavelength 488 nm is produced by organ laser, which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the stopping (cut-off) potential of photoelectron is 0.38 V. Find the work function of the material from which the emitter is made.

• 1.25 eV

• 2.17 eV

• 4.07 eV

• 3.57 eV

A beam of light after reflection on a plane mirror forms a real image. The beam is

• convergent

• divergent

• parallel to axis

• parallel but not to axis of mirror