Question 5: What is resonance? Give three of its examples from our daily life. ANSWER There is always a marked increase in the amplitude of a vibrating body when an external force having the same time period as that of the natural time period of the body is applied to it. This phenomenon is called resonance. It also occurs when the frequency of the applied force is an integral multiple of the natural frequency of the oscillating body, i-e, 2f, 3f, 4f …

### Examples

The antenna of a radio receives thousands of different radio waves. We are, obviously, interested in one of them to listen to. The tuning system of the radio distinguishes the desired frequency for us. The tuning system consists of electronic circuit in the radio, usually a knob on the radio body and a calibrated part showing different readings. Now we are turning the knob on the radio, we are in fact changing the frequency of the receiving antenna. When this frequency equals the transmission frequency of the station we want to listen to, it absorbs maximum energy and we hear that frequency clearly.

#### Swing

Another good example of mechanical resonance is the swinging of a swing. The swing is acting like a pendulum. It goes back and forth with a certain natural frequency of its own. If we apply a force of the same period as that of the natural frequency of the swing, the swing will swing to a maximum amplitude. However, if the applied force is not equal to or any integral multiple of the natural frequency of the swing, it will soon stop. Microwave oven A microwave oven makes use of this phenomenon. Microwaves have long wavelengths of 12 cm and their frequency is 2450 Hz. This frequency matches with the frequency of water molecules. Therefore, when microwaves are passed through water, its molecules start vibration with high amplitudes. This produces high energy and the foods that contain the water molecules is heated up.