Aaaahmmm please help me answer this Question,.. please,.. tnx!^^,..?

Question

1.) Strings of Christmas lights are sometimes made of miniature lamps connected in series. For an eight-lamp 220V set, what is the voltage across each lamp? If one lamp were removed, what would happen? The voltage across the empty socket becomes equal to the line voltage. Why?

2.) As one turns on more lamps in an ordinary household circuit, what happens to the current in the first lamp? To the line current? To the line voltage? Why is it not customary to connect household electric lamps in series?

3.) A piece of copper wire is cut into equal parts. These parts are connected in parallel. How will the joint resistance of the parallel combination compare with the original resistance of the single wire?

4.) Two lamps need 50V and 2A each in order to operate at desired brilliancy. They are to be connected in series across a110V line. What is the resistance of the rheostat which must be placed in series with the lamps?

5.) The rheostat of resistance 10 and 15 ohms are connected in parallel and joined to a battery of negligible internal resistance. There is a current of 0.2 A in the 10 ohm rheostat. Determine (a) the current in the 15 ohm rheostat and (b) the emf of the battery.

Answer 1

1.) Strings of Christmas lights are sometimes made of miniature lamps connected in series. For an eight-lamp 220V set, what is the voltage across each lamp? If one lamp were removed, what would happen? The voltage across the empty socket becomes equal to the line voltage. Why?

220/8 = 27.5 volts

remove one and the rest go out.

Why do you see 220v across the empty socket? because there is no current to lower the voltage.

2.) As one turns on more lamps in an ordinary household circuit, what happens to the current in the first lamp? To the line current? To the line voltage? Why is it not customary to connect household electric lamps in series?

nothing

current goes up as you turn on more loads.

line voltage doesn't change (or should not. It may go down by a volt or two)

Because the voltage would change as you turned lights on and off.

3.) A piece of copper wire is cut into equal parts. These parts are connected in parallel. How will the joint resistance of the parallel combination compare with the original resistance of the single wire?

1/4 th. Each piece is half the resistance of the original piece. Putting the two in parallel cuts the resistance in half again.

4.) Two lamps need 50V and 2A each in order to operate at desired brilliancy. They are to be connected in series across a110V line. What is the resistance of the rheostat which must be placed in series with the lamps?

rheostat, I think you mean resistor.

two in series means the total is 100 v and 2 amps. To get to 110 volts you need to drop 10 volts at 2 amps, which is 5 ohms.

5.) The rheostat of resistance 10 and 15 ohms are connected in parallel and joined to a battery of negligible internal resistance. There is a current of 0.2 A in the 10 ohm rheostat. Determine (a) the current in the 15 ohm rheostat and (b) the emf of the battery.

rheostat, I think you mean resistor.

10 and 15 in parallel are equal to 10*15/(10+15) = 6 ohms

E = IR = 0.2 * 10 = 2 volts

a) I = E/R = 2/15 = 0.133 amps

b) 2 volts, see above.

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