Page 56 - Innovator's Science-8

store, and the smoke they produce can hurt your eyes and make it hard to breathe. Burning them also
releases harmful gases like carbon dioxide and carbon monoxide, which pollute the air and harm the
environment. Electric heaters or stoves are easier to use because they need less space and do not cause
smoke or pollu on.
7. Look at the Figure. If the compass is placed near the
coil deflects:
i. Draw an arrow on the diagram to show the path of
the electric current.

ii. Explain why the compass needle moves when
current flows.

iii. Predict what would happen to the deflec on if you reverse the ba ery terminals.
Ans. i. The current flows from the posi ve terminal of the cell to end
marked A of the coil, then through the coil to end marked B, and
then to the nega ve terminal of the cell as shown by the red
arrows in the Figure.

ii. The compass needle moves as the coil becomes a magnet on
passing the current through it, and the compass needle in its
magne c field moves.
iii. When we reverse the ba ery terminals, the poles of the coil electromagnet change. Therefore, the
deflec on in the compass needle also changes accordingly. The pole of the compass needle that was
earlier a racted to the coil will move away from it, and the other pole of the compass needle will get
a racted towards the coil.

8. Suppose Sumana forgets to move the switch of her li ing electromagnet model to the OFF posi on (in
the introduc on story). A er some me, the iron nail no longer picks up the iron paper clips, but the
wire wrapped around the iron nail is s ll warm. Why did the li ing electromagnet stop li ing the
clips? Give possible reasons.
Ans: A wire coil becomes a magnet only when electricity is flowing through it. Once the electricity stops, it
loses its magne sm. While the current is flowing, some of the electrical energy turns into heat, making
the wire warm. When the current stops, the hea ng also stops, but the wire stays warm for a short me
before cooling down to normal temperature.
9. In Figure (below), in which case, the LED will glow when the switch is closed.

Ans. The LED will glow when the switch is closed in case of (a). Here, the electrolyte is the lemon juice. Copper
and iron plates properly placed in a weak acid or salt solu on and connected in a circuit, produce
electricity. In case of (b), the liquid used is pure water that does not become an electrolyte.

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Science-8