Physics - Study Mode

[#936] Forged documents are detected by
Correct Answer

(A) Ultraviolet rays

Explanation

Solution: Old postcards, books, signs, photos and other paper products made before the late 1930s rarely glow under a black light. Chemical bleaches and dyes used in modern papers will fluoresce under ultraviolet light. Knowing this helps to detect forged documents and distinguish reproductions in all types of ephemera.

[#937] The radiation initially produced in fluorescent tube is
Correct Answer

(B) Ultraviolet

Explanation

Solution: The primary radiation that is initially produced within a fluorescent lamp is analogous to that emitted by a low pressure mercury lamp. Fluorescent lamps produce UV radiation by ionizing low-pressure mercury vapour. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.

[#938] In a vacuum, all electromagnetic waves have the same
Correct Answer

(A) Velocity

Explanation

Solution: When traveling in a vacuum, electronic waves from the electromagnetic spectrum all travel at the same speed. Velocity is speed with direction, so they would all travel at the same velocity, relatively speaking. But frequency and wavelength are quite different.

[#939] Ultra violet radiations of the Sun do not reach the earth because, earth's atmosphere is surrounded by
Correct Answer

(D) Ozone

Explanation

Solution: Ultra violet radiations of the Sun do not reach the earth because, earth's atmosphere is surrounded by Ozone.

[#940] Which one among the following is not an electromagnetic wave?
Correct Answer

(C) Cathode Ray

Explanation

Solution: In physics, electromagnetic radiation (EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-ray, and gamma radiation.