Luke's Physics Questions thread!

[lukew]

I keep on asking for help so I figured I might start a question thread.

I know these are easy questions but I have blanked out and it'd be great if someone could explain to me how to do the following:

1. How much current is drawn by a 6W torch globe that utilises two 1.5v batteries in series?
A- O.5 Amps
B- 4.0 Amps
C- 9.0 Amps
D- 2.0 Amps

2. What is the resistance of a resistor which has 3.5 Amps passing through it and a voltage of 2.5 Volts is applied to it?
A- 8.75 Ohms
B- 0.71 Ohms
C- 1.4 Ohms
D- 6.0 Ohms

3. How much energy will a globe use in 4 hours of operation (Battery has an EMF of 9.0V) ?

[moekamo]

1) P=IV, power is 6W, voltage is 1.5 + 1.5 = 3 since the batteries are series so I=P/V= 6/3 = 2Amps
D

2) V=IR, voltage is 2.5 volts, current is 3.5 amps so R=V/I = 2.5/3.5 = 5/7 (or 0.71) ohms
B

3) E=Pt = V^2/R *t = 9^2 * 4*60*60 / R, what is the resistance? without it you cant get the energy...

[lukew]

Sorry, that's part of a question I didn't fully write out.

3. A battery in a circuit has current of 4.5 Amps passing through it
a) How many coulombs of charge pass through the battery in 5 seconds

b) If the battery has an EMF of 9.0 Volts, how many joules of energy does it provide to the circuit each second

C) How much energy will a 200 W globe use in 4 hours of operation

[schnappy]

a. 4.5 * 5 (Amps is coulombs per second)

b. 9 J (1 V = 1 J per C)

c. 200*60*4 (Power is Joules per second, just convert hours to seconds)

[lukew]

sweet, thanks

[lukew]

I have to write a prac report on some statistics I found while running an electric circuit with resistors, globes, ammeters, and voltmeters.
I'm just not sure what I'm required to write about?

Write a detailed discussion
- identifying ALL the key physical relationships occurring
- Contrasting your experimental results with the theoretical outcomes, offering explanations for any deviations
- and suggest one extension to the practical activity to further your understanding

If anyone could unpack those questions and explain what I'm expected to summarise that would be veeery helpful.

[moekamo]

ummm, what exactly were you measuring, and what were you controlling?

for the first part, you probably have to discuss how the voltage was related to the current experimentally, i.e linear relationship or whatever you found...

then compare to what is the predicted current/voltage for a certain voltage/current based on your resistance value and the V=IR formula,

then think of something to do that would help you understand it more, i dont know how many resistors you had, but i guess you could do 2 or more in series/parallel to find out what happens to voltage/current applied

but yea... hope this helped...

[lukew]

Thanks it did