Topic outline

• Electricity and Circuits

Q51. Differentiate between open and closed circuit.

Ans. An open circuit is one where the continuity has been broken by an interruption in the path for current to flow. For example: a string of electric lights that don't work if one of the bulbs goes out.

A closed circuit is one that is complete, with good continuity throughout. For example: a circuit connected to a dead battery may not perform any work, but it is still a closed circuit.

Q52. What do the danger sign on poles and electric substation indicate? What measure should we take for all activities related to electricity?

Ans. Danger sign displayed on poles and electric substation to warn people that electricity can be dangerous if not handled properly. Carelessness in handling electricity and electric devices can cause severe injuries and sometimes even death.

We should use only electric cells for all activities related to electricity.

Q53. How does an electric light bulb work?

Ans. When the current flow through the bulb, the filament of the bulb glows and produces light. The inert gas inside the glass helps prevent the filament from becoming too hot and breaking. If there is any kind of breakage in the filament, it means that the thin coil inside has snapped and therefore electricity cannot flow completely through the circuit and the bulb will not glow. Such a bulb is said to be fused and needs to be replaced.

Q54. Explain the structure of an electric bulb using diagram.

Ans. The thin wire that gives off light is called the filament of the bulb. It is usually made up of metal called tungsten. The filament is fixed to two thicker wires, which also provide support to it. One of these thick wires is connected to the metal case at the base of the bulb. The other thick wire is connected to the metal tip at the centre of the base. The base of the bulb and the metal tip of the base are the two terminals of the bulb. These two terminals are fixed in such a way that they do not touch each other.

Q55. For each arrangement, find out whether the bulb glows or not.

Circuit is complete. Therefore, bulb will glow.

Circuit is not complete. Therefore, bulb will not glow.

Circuit is open or broken. Therefore, bulb will not glow.

Circuit is not complete. Therefore, bulb will not glow.

Circuit is open or broken. Therefore, bulb will not glow.

Circuit is complete. Therefore, bulb will glow.