Which of the following are the characteristics of electromagnetic waves? 1. They are elastic waves. 2. They can also move in vacuum. 3. They have electric and magnetic components which are mutually perpendicular. 4. They move with a speed equal to 3 lakh meters per second. Select the correct answer using the code given below:
- A.1, 2, 3 and 4
- B.1, 2 and 4 only
- C.2 and 3 only
- D.3 and 4 only
Correct answer
Explanation
The correct answer is C, 2 and 3 only. Electromagnetic waves need no medium, so they travel through vacuum, and they consist of electric and magnetic fields that oscillate at right angles to each other and to the direction of travel. Statement 1 is wrong: elastic or mechanical waves, such as sound, need a material medium whose particles vibrate, while electromagnetic waves are oscillating fields. Statement 2 is correct, which is why sunlight crosses empty space to reach the Earth. Statement 3 is correct; electromagnetic waves are transverse. Statement 4 is wrong because their speed in vacuum is about 3 lakh kilometres per second, not 3 lakh metres per second. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays all belong to this family. Option A is wrong because it includes the false statements 1 and 4. Option B is wrong because it includes statements 1 and 4 and leaves out the correct statement 3. Option D is wrong because statement 4 is false and statement 2 is left out. Exam tip: EM waves = transverse, no medium needed, c ≈ 3 × 10^8 m/s in vacuum.
Practice Questions
View allIn the joining of railway tracks, iron oxide is made to react with
- A.Aluminium
- B.Zinc
- C.Copper
- D.Tin
Show answer
Railway tracks are joined by the thermite process, in which aluminium powder reduces iron oxide to molten iron. The reaction is Fe₂O₃ + 2Al → 2Fe + Al₂O₃.
Read the full explanation →If atomic number of an element is 11, the correct name, symbol and valency are :
- A.Lithium, Li, 1
- B.Magnesium, Mg, 2
- C.Boron, B, 3
- D.Sodium, Na, 1
Show answer
The element with atomic number 11 is sodium, and with one electron in its outermost shell its valency is 1.
Read the full explanation →A car of mass 800 kg is travelling at a speed of 40 km/h on a straight road. A force of 1000 N is applied on it in the direction of its velocity for 12 s. Which one among the following is the final speed of the car?
- A.55 km/h
- B.60 km/h
- C.94 km/h
- D.104 km/h
Show answer
The force gives the car an extra 15 m/s, which is 54 km/h, and 40 + 54 = 94 km/h. By Newton's second law, acceleration a = F/m = 1000 N ÷ 800 kg = 1.25 m/s².
Read the full explanation →Consider the electromagnetic radiations having wavelengths 200 nm, 500 nm and 1000 nm. Which wavelength(s) of the following can make visual sensation to a human eye?
- A.200 nm and 500 nm
- B.500 nm and 1000 nm
- C.500 nm only
- D.200 nm and 1000 nm
Show answer
The human eye responds only to visible light, which lies roughly between 400 nm (violet) and 700 nm (red), and 500 nm is the only one of the three values in that range.
Read the full explanation →Bright light is found to emit from photographer's flashgun. This brightness is due to the presence of which one of the following noble gases?
- A.Argon
- B.Xenon
- C.Neon
- D.Helium
Show answer
A photographer's flash tube is filled with xenon, which gives an intense burst of white light when a high-voltage spark passes through it.
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