Isaac Physics Essential Pre-Uni Physics C6a

Could anyone give me a hand with these questions please?

https://isaacphysics.org/questions/phys19_c6a_q5?board=phys19_c6_add&stage=a_level
(only Part B)

https://isaacphysics.org/questions/phys19_c6a_q7?board=phys19_c6_add&stage=a_level

https://isaacphysics.org/questions/phys19_c6a_q8?board=phys19_c6_add&stage=a_level

https://isaacphysics.org/questions/phys19_c6a_q10?board=phys19_c6_add&stage=a_level

Reply 1

CorporalBooch43

9

Hi, I am doing Isaac physics now as well😂 can you send a picture of your questions?

Reply 2

katieh1301

3

For the first q (part B) you want to use the voltage across the 7.6 ohm resistor as well as your answer to part A to figure out the voltage across the other two resistors--this will be the same for both of them as voltage is the same in parallel. Then you can work out the current across the 6.0 ohm resistor. If you know the current across the 7.6 ohm resistor, which you hopefully worked out in part A, you can then use these two currents to find the current across the X ohm resistor (think Kirchoff's laws/conservation of charge). And then if you know the current and voltage you can work out resistance :smile:

hope this made sense let me know if any of that is unclear

Reply 3

katieh1301

3

For the second q:
Find emf using E=I(r+R) then use that equation again with the new current of 4.0A to find the new value of R--this will be the total resistance of the two resistors in series which will just be equal to 0.50 + X
For the third q:
Find the resistance of your original resistor. When the new resistor is in parallel the 0.40A current will be shared across both resistor - use I = V/R to find the current on the original resistor, the current on the new resistor will be 0.40 - (current on original resistor). Then you will have the voltage and current across this resistor so can calculate resistance :smile:

For the fourth q:
Use E=I(r+R) to find the total resistance R in the circuit, then use the rule for total resistance of resistors in parallel to solve for X.

Reply 4

Mainey372

3

Original post by katieh1301

For the first q (part B) you want to use the voltage across the 7.6 ohm resistor as well as your answer to part A to figure out the voltage across the other two resistors--this will be the same for both of them as voltage is the same in parallel. Then you can work out the current across the 6.0 ohm resistor. If you know the current across the 7.6 ohm resistor, which you hopefully worked out in part A, you can then use these two currents to find the current across the X ohm resistor (think Kirchoff's laws/conservation of charge). And then if you know the current and voltage you can work out resistance :smile:

hope this made sense let me know if any of that is unclear

How do you answer part A? I've been stuck on it for a while

Original post by Mainey372

How do you answer part A? I've been stuck on it for a while

Do you know E - Ir = IR?

R is the external resistance and r is the internal resistance.

The terminal p.d. is E - Ir.

You are given the potential difference across the 7.6-Ω resistor is 1.52V, so you can find the current in the internal resistor and then apply E - Ir.

Reply 6

Onyeka.

1

Original post by Eimmanuel

Do you know E - Ir = IR?
R is the external resistance and r is the internal resistance.
The terminal p.d. is E - Ir.
You are given the potential difference across the 7.6-Ω resistor is 1.52V, so you can find the current in the internal resistor and then apply E - Ir.

i had 2 as my EMF and 0.5 for r (internal resistance) and got 0.96 for current which gave me 1.52 im so lost

(edited 1 month ago)

Reply 7

mosaurlodon

10

You basically have 4 resistors - 2 in parallel, the 7.6ohm resistor and a resistor of 0.5ohms to represent the internal resistance.
You can calculate the current through the 7.6 ohm resistor and you know this will be the same through the 0.5ohm resistor since they're in series.
Then you know that the emf is 2V
the pd across the terminals is the emf minus the 'lost volts' from internal resistance
You can work out 'lost volts' using v=ir :smile:

Original post by Onyeka.

i had 2 as my EMF and 0.5 for r (internal resistance) and got 0.96 for current which gave me 1.52 im so lost