2018 A/L Physics Past Paper · Question 03 (English Medium)

Transverse and longitudinal waves

Which of the following statements is not true?

(1) LASER light consists of transverse waves.
(2) Gamma rays are transverse waves.
(3) Primary waves (P-waves) travelling through the crust of the Earth are longitudinal waves.
(4) Ultrasound waves are longitudinal waves.
(5) FM waves are longitudinal waves.

Answer and explanation

Answer: (5) FM waves are longitudinal waves.

What the question asks

Four statements give the right wave type. One gives the wrong type.

Find the one that is not true.

There are two types of progressive waves called transverse and longitudinal.

Since, electromagnetic waves undergo polarization these waves are seen to behave as transverse waves.

These waves propagate longitudinally as sound waves.

The main difference between these waves and the P waves is that these waves are transverse.

FM waves are radio waves. Radio waves are electromagnetic waves.

Electromagnetic waves can be polarized. So they are transverse.

So "FM waves are longitudinal waves" is not true.

LASER light, gamma rays and FM waves are electromagnetic waves. They are transverse.

P waves and ultrasound are like sound. They are longitudinal.

Only option (5) gives the wrong wave type.

LASER light is an electromagnetic wave. So it is transverse.

The statement is true.

Gamma rays are electromagnetic waves. So they are transverse.

P waves travel like sound waves. They are longitudinal.

Ultrasound is sound too high for us to hear. Sound waves are longitudinal.

FM waves are electromagnetic waves. So they are transverse.

The statement that is not true is (5).

In a "not true" question, mark each statement true or false.

Then choose the false one.

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