Basically an electrical filter is a circuit that can be designed to modify,reshape or reject unwanted frequencies of an electrical signal. For this article we use two circuits (RC and RL) to detect low and high pass filter. Filters are so named according to the frequency range of signals that they allow to pass through them, while blocking or ‘attenuating’ the rest.

Cut-off Frequency: In electrical engineering cut-off frequency is a break point in a system’s frequency.

High Pass Filter: Allow only that frequencies to pass which are greater than cut-off frequency.

Low Pass Filter: Allow only that frequencies to pass which are less than cut-off frequency.

rc Circuit

In RC circuit the basic components are resistor and capacitor so what we have to do with them? We have to make a series circuit in which we see there response for different frequencies. If R = 1.5kΩ and C = 0.01µF

cut-off frequency = 1 / 2 π RC

= 1 / 2 π (1.5k)(0.01µ)

ƒ= 10.610 kHz

In this figure voltmeter is connected with capacitor after taking 10 observations then we connect DMM with resistor again same thing. so we obtain a table

No. of obs. Frequency






1 200 0.2 3.16
2 500 0.36 3.11
3 1k 0.52 3.10
4 5k 1.03 3.03
5 10k 2.31 2.64
6 10.61k 2.31 2
7 20k 2.75 1.24
8 30k 2.92 1.03
9 50k 2.96 0.68

We are concluding two main things from above table first for low frequency our all load is across capacitor but when we increase freq. load start decreasing second for high freq. our all load is across resistor. For HPF frequencies greater than 10.61k can pass and for LPF freq. lower than 10.61k can pass.

Note: RL circuit is same as above experiment but totally opposite we can calculate its cut-off frequency by using formula ƒ= 2 π f L.