Q vs q as a symbol for charge

Hi! What is the difference between capital Q and small q as a symbol for charge? I was told it is something to do with the time constant but I didn't quite get it.

Reply 1

richmaths

Usually Q represents the source charge that generates the electric field and q is the test charge in the electric field. It's similar to M being the mass of the planet and m being the test mass in the gravitational field.

Reply 2

sarah630

Original post by richmaths

Ah okay. Thank you!

Reply 3

Eimmanuel

Study Forum Helper

Original post by sarah630

Hi! What is the difference between capital Q and small q as a symbol for charge? I was told it is something to do with the time constant but I didn't quite get it.

It really depends on the context of the content.

In a resistor-capacitor circuit, capital Q is used to represent the maximum charge on the capacitor or initial charge on the capacitor while the small q is the charge on the charging capacitor or discharging capacitor as a function of time.