# Calculate capacitance to adjust current in ac circuit

• krhisjun
In summary, the conversation discusses how to calculate the value of pure capacitance needed to adjust the current flow in a purely resistive 100W, 110V lamp supplied by an AC source of 230V RMS at 50Hz. The suggested approach is to first calculate the total resistance needed to limit the current to the correct value, and then separate this into resistance and capacitive reactance. The final step is to use the formula for calculating capacitance from capacitive reactance and frequency.

## Homework Statement

A Purely resistive resistive 100w, 110v lamp is to be supplied by an a.c. source of 230v r.m.s at 50Hz. what value of pure capacitance could be put in series to adjust the current flow to a suitable value?

## Homework Equations

p=iv
q=cv
v=ir
i know a number of other time dependant equations but i don't want to list them all pointlessly

## The Attempt at a Solution

Im not sure of how best to approach this, i don't have much experience with AC circuits. i know the current at the lamp is 0.909 amps, from p =iv. but id appreciate a push in the right direction

cheers,khris

If you were to add a resistor to limit the current instead of a capacitor, could you calculate how much total resistance is needed to limit the current to the correct value?

Do you know how are reactances and resistances added?

Can you do that process in reverse separating the total impedance needed (calculated in the first step) into resistance and capacitive reactance.

Can you calculate capacitance from capacitive reactance and frequency?

## What is capacitance?

Capacitance is the ability of a system to store an electric charge. It is measured in farads (F).

## How does capacitance affect current in an AC circuit?

Capacitance and current are inversely proportional in an AC circuit. As capacitance increases, current decreases, and vice versa.

## How do you calculate capacitance to adjust current in an AC circuit?

The formula for calculating capacitance in an AC circuit is C = I / (2πfV), where C is capacitance in farads, I is current in amps, f is frequency in hertz, and V is voltage in volts.

## Are there any other factors that can affect current in an AC circuit besides capacitance?

Yes, other factors such as resistance and inductance can also affect current in an AC circuit. These factors can be calculated using Ohm's law and the formula for inductive reactance, respectively.

## Can capacitance be adjusted to control current in a DC circuit?

No, in a DC circuit, capacitance does not affect current as it does in an AC circuit. In a DC circuit, current is primarily affected by resistance and voltage.