# RC Circuit: Charges faster than discharges?

• Frozen Stair
In summary: A capacitor charges when power is applied to it, and it discharges when power is removed. In a circuit, there is also a resistor called the time constant. The time constant tells us how long it will take for the capacitor to charge to its full capacity and how long it will take for it to discharge to zero.In summary, the capacitor charges faster than it discharges in a simple RC circuit. This difference is almost completely accounted for by experimental error.
Frozen Stair

## Homework Statement

This isn't a problem from a textbook, but it is homework.
For a lab in class, we worked with simple RC circuits on breadboards. The strange thing I noticed is that the capacitor always charges faster than it discharges. I know that the Time constant should be T=RC, so I don't understand why the time constants would differ.

Could someone give a plausible explanation for why this is?

I take it it's a small effect - but not accounted for by experimental error?
Take a closer look at the differences between the circuits?

The time constants are different because conditions are different.
The charging circuit has an extra component in it - and, I'm guessing, one of the other components is in a different state.
The details of the components can matter - what is the cap made of? The resistor? The voltage source? How do all these things affect the circuit?

Simon, the difference in time constants is *very* obvious -it can't be accounted for by experimental error.
Strangely, when charging, the time constant calculated from T=RC is accurately depicted in the graph ("nearly" completely charged at 5T). But when discharging, there's a dramatic difference.

I actually can't find the answers to those questions because my class didn't spend much time on the lab. Is there anything that could potentially make a dramatic difference?
I'm just curious.

In the typical setup, the cap discharges through a different path to the charging.
An extra resistance on that path would give a longer time constant for discharge than charge. An uncontrolled resistance like this is called a "stray" resistance. It could be that you discharged the cap through a different physical resistor than you charged it? Even if they are rated the same value, they may be physically different - especially if the equipment is old. Similarly, there may be longer wires on the discharging side of the circuit or some of the connections were bad on that side.

Without knowing the details of the circuit I can only guess.
Also see:

... an electrolytic capacitor requires a bit extra work to polarize the dielectric which can present as a different resistance charging to discharging but I don't know the details off-hand (it's been a while).

Frozen Stair said:
The strange thing I noticed is that the capacitor always charges faster than it discharges.

What was the circuit used?

## What is an RC circuit?

An RC circuit is a type of electrical circuit that contains a resistor (R) and a capacitor (C). The capacitor stores electrical charge, and the resistor controls the flow of current in the circuit.

## How does an RC circuit charge?

When an RC circuit is connected to a voltage source, the capacitor will begin to charge. As the capacitor charges, the voltage across it increases and the current decreases. The capacitor will continue to charge until it reaches the same voltage as the source.

## Why does an RC circuit charge faster than it discharges?

An RC circuit charges faster than it discharges because the capacitor has a higher resistance to current flow than the resistor. This means that it takes longer for the capacitor to discharge than it does to charge.

## What is the time constant of an RC circuit?

The time constant of an RC circuit is the product of the resistance (R) and the capacitance (C) in the circuit. It represents the time it takes for the capacitor to charge or discharge to about 63% of its maximum voltage.

## How can the time constant of an RC circuit be calculated?

The time constant (τ) of an RC circuit can be calculated using the formula τ = RC, where R is the resistance in ohms and C is the capacitance in farads. This formula can be used to determine the charging or discharging time of the capacitor in the circuit.

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