A luminous object is separated from a screen by distance d. A convex lens is placed between the object and the screen such that it forms a distinct image on the screen. The maximum possible focal length of this convex lens is
4d
2d
In the bandgap between valence band and conduction band in a material is 5.0 eV, then the material is
semiconductor
good conductor
superconductor
insulator
Two coherent monochromatic beams of intensities I and 41 respectively are superposed. The maximum and minimum intensities in the resulting pattern are
5I and 3I
9I and 3I
4I and I
9I and I
In a transistor output characteristics commonly used in common emitter configuration, the base current IB, the collector current lC and the collector emitter voltage VCE have values of the following orders of magnitude in the active region
IB and IC both are in µA and VCE in volt
IB is in µA and IC is in mA and VCE in volt
IB is in mA and IC is in µA and VCE in volt
IB is in mA and IC is in mA and VCE in mV
For the radioactive nuclei that undergo either α or β decay, which one of the following cannot occur ?
Isobar of original nucleus is produced
Isotope of the original nucleus is produced
Nuclei with higher atomic number than that of the original nucleus is produced
Nuclei with lower atomic number than that of the original nucleus is produced
The intermediate image formed by the objective of a compound microscope is
real, inverted and magnified
real, erect and magnified
virtual, erect and magnified
virtual, inverted and magnified
The de-Broglie wavelength of an electron is the same as that of a 50 keV X-ray photon. The ratio of the energy of the photon to the kinetic energy of the electron is (the energy equivalent of electron mass is 0.5 MeV)
1 : 50
1 : 20
20 : 1
50 : 1
A glass slab consists of thin uniform layers of progressively decreasing refractive indices RI (see figure) such that the RI of any layer is µ − m Δµ. Here, µ and Δµ denote the RI of 0th layer and the difference in RI between any two consecutive layers, respectively. The integer m =0, 1, 2, 3, ... denotes the numbers of the successive layers. A ray of light from the 0th layer enters the 1st layer at an angle of incidence of 30°. After undergoing the mth refraction, the ray emerges parallel to the interface. If µ = 1.5 and Δµ = 0.015, the value of m is
20
30
40
50
D.
50
An object is placed 30 cm away from a convex lens of focal length 10 cm and a sharp image is formed on a screen. Now a concave lens is placed in contact with the convex lens. The screen now has to be moved by 45 cm to get a sharp image again. The magnitude of focal length of the concave lens is (in cm)
72
60
36
20
Find the correct statement(s) about photoelectric effect.
There is no significant time delay between the absorption of a suitable radiation and the emission of electrons.
Einstein analysis gives a threshold frequency above which no electron can be emitted
The maximum kinetic energy of the emitted photoelectrons is proportional to the frequency of incident radiation.
The maximum kinetic energy of electrons does not depend on the intensity of radiation.