Physics

Electrons and Photons

158 Questions

Electrons and photons are fundamental concepts in modern physics, focusing on quantum interactions and the photoelectric effect. The topic involves calculating work functions, kinetic energy, and photon wavelengths. These physics questions are highly relevant for competitive test preparation.

Photoelectric effectWork function calculationsPhoton energy and wavelengthElectron emissionAtomic transitions

Electrons and Photons Questions

Multiple choice general knowledge science & technology

What process responsible for producing photons in a diode laser?

  1. Fermi level shift

  2. Majority carrier injection

  3. Electron-hole recombination

  4. Carrier freeze out

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Electron-hole recombination is correct. In a diode laser, photons are produced when electrons from the n-type region recombine with holes in the p-type region at the junction, releasing energy as light. Fermi level shift and carrier injection are related processes but not the photon-producing mechanism. Carrier freeze out is a low-temperature phenomenon that reduces conductivity.

Multiple choice general knowledge science & technology

What is emitted by the hot metal filament in a cathode ray tube?

  1. protons

  2. neutrons

  3. electrons

  4. x-rays
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In a cathode ray tube, the hot metal filament (cathode) emits electrons through a process called thermionic emission. These electrons are then accelerated toward the anode, forming the cathode ray. Protons and neutrons remain in the nucleus, and X-rays are produced when electrons strike the target, not emitted by the filament.

Multiple choice

Photo-electric effect is the phenomenon of __________.

  1. ejection of electrons from a metal plate when light of a suitable wavelength falls on it

  2. production of alpha-rays

  3. production of beta-rays

  4. production of gamma-rays
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The photoelectric effect occurs when photons of sufficient energy (above a threshold frequency) strike a metal surface and eject electrons. This phenomenon provided key evidence for quantum theory, showing light behaves as discrete packets of energy (photons). It is not about producing radioactive particles (alpha, beta, or gamma rays).

Multiple choice

Which of the following statements are FALSE regarding Transmission Electron Microscopy (TEM)?

  1. First Transmission Electron microscope was built by Knoll and Ruska.
  2. The electronic beam is focused by electromagnetic lenses.
  3. TEM is capable of imaging at a significantly higher resolution than light microscopes.

  1. Only 1

  2. Only 2

  3. Only 3

  4. 2 and 3

  5. None
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

All are true statements. First TEM was built by Max Knoll and Ernst Ruska in 1931. TEMs are capable of imaging at a significantly higher resolution than light microscopes, owing to the small de Broglie wavelength of electrons. In TEM electrons are accelerated by an electric potential and focused by electrostatic and electromagnetic lenses onto the sample.

Multiple choice

Which of the following statements are correct for work function? (a) It is defined as the energy required for emitting electrons from metallic surface. (b) Its value is generally expressed in joule. (c) It is a characteristic of a metal. (d) The work function for alkali metals is very high.

  1. Both (a) and (b)

  2. Both (a) and (c)

  3. Both (b) and (c)

  4. Both (b) and (d)

  5. Both (a) and (d)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Work function is defined as the energy required for emitting electrons from metallic surface. It is a characteristic of a metal. Both the statements are correct.

Multiple choice

On which of the following factors does the rate of emission of electrons depend?

  1. Surface area of filament

  2. Temperature of filament

  3. Material used for filament

  4. Surface area and temperature of filament, and the material used for filament
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Thermionic emission is the emission of electrons from a heated filament or substance. When a filament like tungsten is heated to a high temperature, some electrons acquire sufficient energy and are able to break away from the surface of material and go into space. So, rate of emission of electrons depends upon surface area and temperature of filament and also on the material used for filament.

Multiple choice

X-rays are produced when

  1. electric current flows through the X-ray tube filament

  2. projectile electrons bounce off the cathode

  3. projectile electrons interact with target atoms

  4. the target angle is sufficiently large
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

X-rays are produced when projectile electrons interact with target atoms.

Multiple choice

When can a steady bright spot be seen on the screen on the deflecting system in a hot cathode ray tube?

  1. When the electron beam strikes the centre of the screen

  2. When no potential difference is applied across the pairs of plates

  3. When there is no fluorescence on the screen

  4. Both (1) and (2)

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When no potential difference is applied across the pairs of plates, the electrons beam strikes the centre of the screen and a steady bright spot is seen due to fluorescence on the screen on the deflecting system in a hot cathode ray tube.

Multiple choice

Which of the following is not true regarding the radiation sources of infrared spectroscopy?

  1. The source of radiation in IR spectroscopy is ideally a black body radiator.

  2. Globar is a silicon carbide rod.

  3. Nernst filament should be externally heated to dull-red hot.

  4. In Globar water cooling of electrical parts are used to prevent arching.

  5. Nernst filament is operated in parallel with ballast resistance in constant voltage circuit.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

This option is correct since Nernst filament has a negative temperature coefficient of electrical resistance, so it is operated in series with ballast resistance in constant voltage circuit.

Multiple choice

Which of the following is not true for a photomultiplier tube (PMT)?

  1. PMTs have high internal gain.

  2. The working of PMT is based upon photoelectric effect.

  3. The material of photocathode is usually a mixture of alkali metals

  4. The dynodes are maintained at successively more negative potential.

  5. The response of a PMT is linear.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This option is correct as the given statement is wrong regarding PMTs since dynodes are additional electrodes which are maintained at successively less  negative potential  which leads to generation of additional electrons thus multiplying the primary current.

Multiple choice

Which of the following statements are correct for work function?

(a) It is defined as the energy required for emitting electrons from metallic surface. (b) Its value is generally expressed in joule. (c) It is a characteristic of a metal. (d) The work function for alkali metals is very high.

  1. Both (a) and (b)

  2. Both (a) and (c)

  3. Both (b) and (c)

  4. Both (b) and (d)

  5. Both (a) and (d)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Work function is defined as the energy required for emitting electrons from metallic surface. It is a characteristic of a metal. Both the statements are correct.

Multiple choice

An intrinsic semiconductor has a band gap of 1.5 eV. The wavelength of the electromagnetic radiation required to cause the material photoconducting is ________________.

  1. 3525 Å

  2. 7827 Å

  3. 8272 Å

  4. 8573 Å

  5. 9368 Å
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given, Band gap (E) = 1.5 eV = 1.5 × 1.602×10-12 erg, h = 6.627 × 10-27 erg.s, c = 3 × 1010 cm/s Now, energy of material, E = hc/λ λ = 6.627 × 10-27 × 3 × 1010/ 1.5 × 1.602×10-12 = 8.272 × 10-5 cm = 8272 Å.

Multiple choice

Which among the following statements is/are true about TEM?

  1. The first Transmission Electron Microscope was built by Knoll and Ruska.
  2. The TEM is capable of imaging at a significantly higher resolution than the light microscopes.
  3. The electronic beam is focused by electromagnetic lenses.

  1. Only 1

  2. Only 2

  3. Only 3

  4. 2 and 3

  5. 1, 2 and 3
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

All are true statements. The first TEM was built by Max Knoll and Ernst Ruska in 1931. The TEMs are capable of imaging at a significantly higher resolution than the light microscopes, owing to the small de Broglie wavelength of electrons. In TEM, electrons are accelerated by an electric potential and focused by the electrostatic and electromagnetic lenses onto the sample.

Multiple choice

Cyclotron is a device which

  1. detects and analyses the spectrum of light emitted by stars

  2. accelerates subatomic particles using combined electric and magnetic fields

  3. detects the cyclic variation in the intensity of electromagnetic radiation emitted from stars

  4. measures the intensity of X-rays
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A cyclotron is a particle accelerator that uses alternating electric fields and static magnetic fields to accelerate charged particles in a spiral path. It is not used for spectroscopy, detecting stellar variations, or measuring X-ray intensity.

Multiple choice

Which of the following statements is/are false?

  1. The d-d transition band occurs only in visible region.
  2. The position of charge transfer band depends on the nature of metal and ligand.
  3. Frequencies greater than 10,000 cm-1 are not accessible experimentally.

  1. Only 1

  2. Only 2

  3. Only 3

  4. 1 and 3

  5. 2 and 3
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This option is correct because d-d transition band occurs not only in visible but also in near infra-red, ultra-violet regions etc.