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Electric Heating Appliances and Bulb
- Heating appliances use a heating element
- The element is a coil of nichrome wire
- It becomes red hot and gives heat
- An electric bulb has a tungsten filament
- The hot filament glows and gives light
- nichrome element becomes red hot
- copper cord stays cool
- gives out heat
- thin tungsten filament of high resistance
- becomes white hot
- emits light
- Filament bulbs waste most electricity as heat, so they are not power efficient.
- Fluorescent tube lights and CFLs have no filament, so they save electricity.
- CFLs and tube lights do not work on the heating effect of current.
Electric Fuse
- A fuse is a safety device
- It prevents fires from excess current
- It works on the heating effect of current
- Made of a thin, low-melting-point wire
- It melts and breaks the circuit
- fitted near the main switch
- excess current heats the thin wire
- it melts and breaks the circuit
- glass tube with thin fuse wire
- used inside TV and fridge
- protects the appliance
- The fuse wire is thin with high resistance, so it heats and melts before the rest of the wiring.
- A thick wire has low resistance, so it will not melt easily — never use it as a fuse.
- MCBs (Miniature Circuit Breakers) are now used in place of traditional fuses.
Name the following: The metal which is used to make the filament of an electric bulb.
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Explanation
- The thin, high-resistance tungsten filament glows white hot and gives light.
Name the following: The full form of CFL.
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Explanation
- A CFL has no filament and saves electricity compared to filament bulbs.
Fill in the blank: When a room heater is switched 'on', its element becomes ________.
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Explanation
- The high-resistance nichrome element produces a lot of heat and glows red hot.
Fill in the blank: The safety device based on the heating effect of electric current is called ________.
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Explanation
- The fuse wire melts when too much current flows, breaking the circuit.
State whether true or false: A compact fluorescent lamp (CFL) has a filament in it.
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Explanation
- A CFL has no filament; that is why it does not waste electricity as heat.
State whether true or false: The heating element of an electric iron is made of tungsten.
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Explanation
- The element of an electric iron is made of nichrome; tungsten is used for bulb filaments.
State whether true or false: Compact fluorescent lamp (CFL) works on the heating effect of current.
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Explanation
- A CFL has no filament and does not work on the heating effect, so it saves electricity.
Give two applications of the heating effect of electric current.
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Explanation
- Electric heating appliances like room heaters and electric irons.
- Electric bulbs that produce light from a hot filament.
- The safety device called an electric fuse also uses it.
Explain why, any metal wire or metal strip cannot be used in place of fuse wire.
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Explanation
- A fuse wire is made of a thin tin-plated copper wire with a low melting point.
- It melts quickly when too much current flows, breaking the circuit.
- An ordinary metal wire has a high melting point, so it will not melt easily and would fail to protect the circuit.
What type of electric fuse is used in individual electrical appliances? Explain with the help of a labelled diagram.
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Explanation
- It is a glass tube with a thin fuse wire sealed inside it.
- The glass tube has metal caps at both ends to connect it in the circuit.
- If a large current flows, the fuse wire melts and breaks, protecting the appliance.
What might happen if a fuse is not inserted in household electric wiring?
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Explanation
- If current becomes too large, there is nothing to break the circuit.
- The wires would heat up to very high temperatures and could cause fires.
- Appliances like TV and refrigerator could also be damaged.
Explain why, filament-type electric bulbs are not power efficient. Name any two types of electric lighting devices which are much more energy efficient than filament-type bulbs.
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Explanation
- In a filament bulb, a major part of the electricity is converted into heat and only a small part into light.
- This wastage makes them power inefficient.
- Fluorescent tube lights and CFLs have no filament, so they waste much less energy.
What is meant by the heating effect of current? Name two appliances which work on the heating effect of current.
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Explanation
- In the heating effect, electric energy is converted into heat energy in a high-resistance wire.
- Electric iron works on the heating effect.
- Electric room heater also works on the heating effect.
The filament of an electric bulb is made of a thin wire of:
- (a) copper
- (b) aluminium
- (c) nichrome
- (d) tungsten
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Explanation
- Tungsten's thin, high-resistance filament glows white hot.
When electric current is passed through the filament of a bulb, it gives off: A. Sound B. Heat C. Magnetism D. Light
- (a) A and B
- (b) B and C
- (c) B and D
- (d) only D
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Explanation
- The filament gives both heat and light; a major part of energy becomes heat.
An electric fuse works on the:
- (a) chemical effect of current
- (b) magnetic effect of current
- (c) lighting effect of current
- (d) heating effect of current
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Explanation
- Excess current heats and melts the thin fuse wire, breaking the circuit.
In a filament-type bulb, a lot of electric energy is wasted in the form of:
- (a) magnetism
- (b) sound
- (c) light
- (d) heat
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Explanation
- Most electricity in a filament bulb becomes heat, only a small part becomes light.
The compact fluorescent electric lamp has:
- (a) nichrome filament
- (b) chromium filament
- (c) tungsten filament
- (d) no filament
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Explanation
- A CFL has no filament, so it does not waste energy as heat.
