Q4. Give two examples of mechanical waves and two of electromagnetic waves.
Mechanical: sound waves, water waves, waves on a string, seismic waves. Electromagnetic: light, radio waves, X-rays.
Q5. How does a sound wave travel through air if the air itself does not flow from the source to the listener?
The source compresses a small region of air. The raised density raises the pressure there, which pushes on the next region and compresses it, while the first region expands. Compressions and rarefactions are passed on from region to region, while each bit of air only moves back and forth a little.
Q6. How far does light travel in a vacuum in one nanosecond (10 s)?
3.00 × 10 × 10 = 0.30 m: about 30 cm.