Why does current flow more easily through a thick wire than a thin wire of the same material when connected to the same source ?
The current flows more easily through a thick wire than through a thin wire. The is because, the than through a thin wire. This is because, the resistance R of a thick wire (large area of cross – section ) is less than that of a thin wire (small area of cross – section) as R ∝ 1/A
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series.
(a) In case of devices in parallel, if one device gets damaged (or open), all others will work as usual as the whole circuit does not break. This is not so with the devices connected in series because when one device connected in series because when one device falls, the circuit breaks and all devices stop working.
(b) Since potential difference across all devices is same in parallel circuit, they will draw required current according to their resistances. This is not so in series circuit where same current flows through in series circuit where same current flows through all the devices, irrespective of their resistance.
Why does the cord of an electric heater not glow while the heating element does ?
The cord of an electric heater is made of thick copper wire and has much lower resistance than the heating element. For the same current (I) flowing through the cord and the element, heat produced in the element is much more than that produced in the cord. As a result, the element becomes very hot and glows whereas the cord does not becomes hot and as such does not glow.
Q. Oil spreads over the surface of water, whereas, water does not spread over the surface of oil. Why?
Ans. The surface tension of the water is more than of oil. Therefore, when oil is poured over water, the greater value of surface tension of water pulls the oil in all direction and as such it spreads on the water. On the other hand, when water is poured over oil, it does not spread over it because the surface tension of oil being less than that of water, it is not able to pull water over it.
Q. It is advised not to stand near a running train. Why?
Ans. When fast moving train passes on a rail, than the velocity of air streams in between the rail and the person standing near rail will be very large as compared to the velocity of air streams on the other side of person away from the rail. According to Bernoulli’s theorem, the pressure of air will become low in between person and rail and is high on the other side of person. As a result of the pressure difference, a thrust acts on the person which may push the person towards rail side and the person may meet with an accident