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# Capacitor charging

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1. Please could someone explain why there is a resistor in capacitor circuits when the capacitor in CHARGING?

I've looked online but I don't really understand the answers I found.

Thanks
2. (Original post by PhyM23)
Please could someone explain why there is a resistor in capacitor circuits when the capacitor in CHARGING?

I've looked online but I don't really understand the answers I found.

Thanks
Practically - to limit the current which otherwise would be high... reduce RF spikes which might interfere with other parts of the circuit.

for exam questions - largely because the formulae don't give sensible answers when R=0
3. (Original post by Joinedup)
Practically - to limit the current which otherwise would be high... reduce RF spikes which might interfere with other parts of the circuit.

for exam questions - largely because the formulae don't give sensible answers when R=0
Thanks for the response!

Please may you explain what you mean by 'RF spikes', and how they interfere with other parts of the circuit?
4. (Original post by PhyM23)
Thanks for the response!

Please may you explain what you mean by 'RF spikes', and how they interfere with other parts of the circuit?
when charging a capacitor through a very low resistance you get a high current flowing for a very short period of time, if you graphed current against time it'd have a very steep gradient - which means high frequency, high frequency electric current means radio transmitter.

it'd interfere with nearby analogue radio receivers and might cause unexpected behavior in digital circuits.

I don't think you'll get any questions on this at A level though

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