Physics

Electromagnetic Waves and Spectrum

670 Questions

Electromagnetic waves and spectrum questions test a candidate's understanding of radiation frequencies, wavelengths, and the properties of different rays like infrared, ultraviolet, and visible light. Concepts also cover practical applications in astronomy and the fundamental speed of light calculations. This physics topic appears regularly in general science sections of major competitive examinations.

UV rays propertiesElectromagnetic radiation frequencyWavelength identificationSpeed of light calculationsBlack body radiation

Electromagnetic Waves and Spectrum Questions

Multiple choice

The spectrum from a black body radiation is called _________.

  1. line spectrum

  2. parallel spectrum

  3. continous spectrum

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A black body is an idealized physical body that absorbs all incident electromagnetic radiation. When it emits radiation, it does so across a full, continuous range of wavelengths rather than at specific discrete lines.

Multiple choice

Electromagnetic radiation is emitted

  1. only by T.V & radio antenna

  2. only by bodies at higher temp. than surrounding

  3. only by bodies at lower temp. than surrounding

  4. by all bodies
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All objects with a temperature above absolute zero (0 Kelvin) emit electromagnetic radiation. This is due to the thermal motion of charged particles within the atoms of the material.

Multiple choice

The energy radiated per second by a spherical black body will be double, if its

  1. radius is increased by nearly 41.5 %

  2. radius is doubled

  3. radius is increased by nearly 44.5 %

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Radiated power is proportional to surface area, which for a sphere is 4 * pi * r^2. To double the power, the area must double, requiring the radius to increase by a factor of sqrt(2) (approx. 1.414), which is a 41.4% increase.

Multiple choice

Which of the following statements is wrong?

  1. Light travels faster in vacuum than in air.

  2. The wavelength of light is longer than the wavelength of sound.

  3. Light travels nearly 330 metres in one second.

  4. Speed of sound is mach one.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The wavelength of light is longer than the wavelength of sound.

Multiple choice

Which statement is not true about sunlight?

  1. Gamma rays are shorter in wavelengths than the visible light.

  2. Only the visible portion of sunlight is used in photosynthesis.

  3. Photons of ultraviolet light contain low energy, and so are harmless to cells.

  4. Shorter wavelengths of radiation contain more energy than longer wavelengths.

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ultraviolet (UV) light is high-energy radiation, not low-energy. It is harmful to cells because it can damage DNA, which is why it is not considered harmless.

Multiple choice

Light travels at a speed of

  1. 400, 000km/second

  2. 200, 000km/second

  3. 300, 000km/second

  4. 600, 000km/second
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The speed of light in a vacuum is approximately 299,792 kilometers per second, which is commonly rounded to 300,000 km/s in educational contexts.

Multiple choice

Energy moving in waves through spaces is known as

  1. electromagnetic radiation

  2. inertia

  3. potential energy

  4. kinetic energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electromagnetic radiation consists of waves of the electromagnetic field, which propagate through space carrying radiant energy. Inertia, potential energy, and kinetic energy describe properties or states of matter rather than the wave-based movement of energy through space.

Multiple choice

Which of the following statements is wrong?

  1. All photons do not carry the same amount of energy

  2. The energy of radiation increases with decrease in the wavelength

  3. The energy of radiation increases with increase in the wave number

  4. None of these

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

All the given statements are correct.

Multiple choice

The approximate velocity of light is

  1. 3x106 m per second

  2. 3x108 m per second

  3. 3x1010 m per second

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The speed of light in a vacuum is approximately 300,000,000 meters per second, which is written in scientific notation as 3 x 10^8 m/s.

Multiple choice

In which case, the wavelength emitted is minimum?

  1. An electron jumps from 2nd to 1st level

  2. An electron jumps from 3rd to 2nd level

  3. An electron jumps from 4th to 3rd level

  4. An electron jumps from 5th to 4th level
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  Applying the Rydberg's equation 1/λ = R0[1/n12 - 1/n22] . We get 1/λ = R0 [3/4] or λ = 1.33/R0. This value of wavelength is the least among the given options.