- This topic has 3 replies, 2 voices, and was last updated 2 days, 22 hours ago by
.
-
Posts
-
Hello Pete,
I’m struggling with question 9 on the RSGB mock test three. It is a circuit diagram.
Both C and D look correct to me. The answer key shows that D is correct.
When I build it on DC circuit builder it shows both are the same.
Please can you explain why C is incorrect? I’m clearly missing something.
Thank you,
KathNo problem, and yes, this is a messy one.
You can remove R1 and R2 as red herrings.
Essentially, you’re left with the standard “parallel” drawing from the course – this one:
https://www.essexham.co.uk/courseimg/circuit-parallel_5dee3982d6999.png
Where a power supply feeds more than one component (e.g. two lamps, or in this case, 2 resistors), the voltage is the same, and the supplied current is the sum of the currents through the individual components.
Just like the example in the course, each lamp has a direct connection, so each gets the full voltage. Half of the circuit’s total current flows through each of the two bulbs.
Correct answer is D – the current over R3 and R4 will be different (as they are different values), but the voltage across the circuit will be the same. It it was a 3 volt battery, all four resistors would have 3v going across them, but different currents.
Does that help?
Pete
- You must be logged in to reply to this topic.