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Science · 2025 · 4 marks
CBSE 2025 · Region 1 · Set 1 · Q39
In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by…
In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is $\displaystyle 220$ V.
(a)
Write the colours of the insulation covers of the line wires through which supply comes to our homes.
(b)
What should be the current rating of the electric circuit ($\displaystyle 220$ V) so that an electric iron of $\displaystyle 1$ kW power rating can be operated ?
(c)(i)
What is the function of the earth wire ? State the advantage of the earth wire in domestic electric appliances such as electric iron.
OR
(c)
(ii)
List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.
Marking-scheme solution
(a)
Live wire - Red
Neutral wire - Black
(b)
Power, \(\displaystyle P = 1 \mathrm{~kW} = 1 \times 1000 \mathrm{~W} = 1000 \mathrm{~W}\)
Voltage, \(\displaystyle V = 220 \mathrm{~V}\)
Current drawn \(\displaystyle I = ?\) \(\displaystyle P = V \times I\)
\[I = \frac{1000 \mathrm{~W}}{220 \mathrm{~V}} = 4 \cdot 54 \mathrm{~A}
\]
Current rating should be of 5A.
(c)(i)
The earth wire provides a low resistance conducting path for the current which ensures that any leakage of current to flow to the metallic body of the appliances, keeps its potential to that of the earth.
The user will not get an electric shock.
OR
(c)
(ii)
Fuse wire
Earth wire
A fuse in a circuit prevents damage to the circuit due to overloading.
Earth wire prevents electric shock due to leakage of current.
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CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.