(a) what is the rate at which energy being delivered to a light bulb higher : just after it is turned on , the glow of the filament is increasing , or after it has been on for a few seconds and the glow is steady ?
(b) IF a piece of wire is used to connect points `b and c` in Fig. 7.9, does the brightness of bulb `R_(1)` increase , decrease or stay constant ? What happens to the brightness of bulb `R_(2)` ? `(I_(1) = I_(2) = I)`
(c) Compare the brightness of four identical light bulbs in ` Fig. 7.10`. What happens if the bulb `A` fails so that it cannot conduct ? What if `C` fails ? What if `D` fails?
(d) If electric power is transmitted over long distances, the resistance of the wires becomes significant. Why ? Which mode of transmission would result in less energy losss: high current and low voltage or low current and high voltage ? Discuss.
(e) In `Fig. 7.11`, describe wha happens to the light bulb after the switch is closed . Assume the capacitor has a large capacitance and is initially uncharged.
(f) Astuident claims that a second light bulb in series is less bright than the first , because the first bulb uses up some of the current . How would you respond to this statement ?
(g) If you were to design an electeric heater using nichrome wire as the heating element , what parameters of the wire would you vary to meet a specific power output , sch as `1000 W`?

Explanation

(a) Just after it is turned on , the energy supplied to the bulb is higher . Becsause initially resistance is low and it increases with the increase in temperature.
(b) After connecting `b and c`, `R_(2)` will be short - circuited . Hence , it will not glow. Now , entire potential difference will be on `R_(1)`. So brightness of `R_(1)` increases.
(c) `D` is short - circuited, so `D` will not glow. Potential difference across `C` is `V`, so potential difference across each of `A and B is V//2`. So brightness of `C` is the greatest and that of `A and B` are equal.
If `A` fails, `B` will not glow. No effect on `C and D`.
IF `C` fails , `C` will not glow. No effect on `A, B , and D`.
IF `D` fails , no effect anywhere.
Because resistance is directly proportional to length , at low current and high voltage energy , loss will be less. Because if current is less , then loss of energy `I^(2)R` will be less.
(e) Initially , current will be high in the circuit , so bulb will glow with maximum possible brightness of the bulb falls and finally the bulb goes out.
(f) This is not true. Because in series, current through all the bulbs is the same. The current is simultaneously set up is series through all the bulbs.
(g) `P =(V^(2))/(R) = (v^(2)A) /(pl)`
Here, `P` and `V` are fixed. We can vary `A` or `l`.