Modern Physics CDS Questions

CDS Physics

Modern Physics MCQ Questions


7.
According to the experimentally observed characteristics of the photoelectric effect, increasing the FREQUENCY of incident light (above the threshold frequency) results in:
A.
A decrease in the number of photoelectrons emitted, regardless of intensity
B.
An increase in the work function of the metal itself
C.
An increase in the maximum kinetic energy of the emitted photoelectrons
D.
No effect whatsoever on the photoelectrons emitted
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ANSWER :
C. An increase in the maximum kinetic energy of the emitted photoelectrons
8.
Which of the following observed characteristics of the photoelectric effect could NOT be satisfactorily explained by the classical wave theory of light, and required Einstein's quantum (photon) explanation instead?
A.
The existence of a threshold frequency, below which no photoelectric emission occurs regardless of light intensity
B.
The fact that light can be reflected from a smooth surface
C.
The fact that light travels in straight lines in a uniform medium
D.
The fact that light can be refracted when passing between different media
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ANSWER :
A. The existence of a threshold frequency, below which no photoelectric emission occurs regardless of light intensity
9.
Photoelectric emission of electrons from a metal surface, upon exposure to light of sufficiently high frequency, occurs essentially:
A.
Only after the metal has been exposed to light for at least several hours
B.
Instantaneously, with no significant measurable time delay (consistent with the particle/photon model of light)
C.
Only after a significant and measurable time delay, often lasting several seconds or longer
D.
Only when the light source is physically touching the metal surface
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ANSWER :
B. Instantaneously, with no significant measurable time delay (consistent with the particle/photon model of light)
10.
Photocells (or photoelectric cells), devices that operate based on the photoelectric effect, are commonly used in practical applications such as:
A.
Measuring atmospheric pressure
B.
Generating nuclear power exclusively
C.
Automatic streetlights and burglar alarm systems, which respond to changes in incident light
D.
Converting sound waves into electrical signals
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ANSWER :
C. Automatic streetlights and burglar alarm systems, which respond to changes in incident light
11.
J.J. Thomson's 'Plum Pudding Model' of the atom, proposed in 1904, envisioned the atom as:
A.
A collection of neutrons only, with no charge at all
B.
A sphere of uniformly distributed positive charge, with negatively charged electrons embedded within it
C.
A small, dense, positively charged nucleus surrounded by orbiting electrons
D.
A completely empty space with no charge of any kind present
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ANSWER :
B. A sphere of uniformly distributed positive charge, with negatively charged electrons embedded within it
12.
Ernest Rutherford's famous gold foil experiment (1909-1911) led to the discovery of:
A.
The electron itself, as a fundamental subatomic particle
B.
The neutron, as a fundamental subatomic particle
C.
The wave nature of the electron
D.
The atomic nucleus, a small, dense, positively charged core at the centre of the atom
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ANSWER :
D. The atomic nucleus, a small, dense, positively charged core at the centre of the atom