ELECTRIC CURRENT AND ITS EFFECTS

I Fill in the blanks :

1. A thin wire in the bulb that glows when an electric current passes through it is called the ____________________.

2. When the bulb gets _______________, its filament is broken.

3. The coil of wire in an electric heater is known as ________________.

4. The amount of heat produced in a wire depends on its, ______________, ________________ and __________________.

5. When an electric current flows through a wire, it behaves like a _________________.

6. The ___________of an electric bell acts as an electromagnet in its working.

II State whether the following statements are True or False :

1. When the electric current is switched off, the coil generally loses its magnetism.

2. The wires used for making electric circuits do not normally become hot.

3. The filament of an electric bulb never gets heated.

4. In a battery, the electric cells are always placed one after the other.

5. Connecting many devices in a single socket does not affect the flow of current in a circuit.

6. Wear and tear of insulated wires can cause short circuits.

7. CFLs consume more electricity than ordinary bulbs

QUESTION ANSWERS

.1 What do mean by heating effect of current? Ans--When current flows through a metal wire it gets heated up, this is called heating effect of current. e.g. a glowing electric bulb becomes warm

2 What are filaments of a bulb and a heater made up of?

 Ans--In a bulb there is a thin wire called the filament made up of tungsten. When current passes through it, it glows and gets heated up. In a heater there is a coil of wire called element which is made up of nichrome. When current passes through element it becomes red hot and give out heat.

 3 What are the factors on which amount of heat produced depends? 

--The amount of heat produced in a wire depends on 

-(A) Its material – better conductors produce less heat; e.g. Elements of electric appliances are made of nichrome whereas connecting wires are made up of copper which is a better conductor so they do not get heated up as the element. -

(B) Its length – as length increases heat produced increases; e.g. elements are coiled in heaters to increase length . 

-(C) Thickness – as thickness increases heat produced decreases; e.g. lead wires of iron, heater etc. are thicker than normal connecting wire so that they don’t get heated up easily.

 4 What is an electric fuse?

 Ans---Electric Fuse - A Safety device in domestic circuit used to prevent electrical fire due to short circuit or overloading.