5L30.36-High Pass / Low Pass Filter

Description: This demonstration allows students to see the effects an inductor and capacitor have on an AC source.

Equipment:

• Speaker with speaker cable
• Radio tuned to either a station or pink noise
• Decade capacitor box
• Decade inductor box
• Two SPDT switches
• Cables to connect components according to the schematic
• Two C clamps to attach the switches to the table

Setup Procedure:

1. Connect the components according to the schematic.
2. Verify that everything is correctly connected and working.
3. Leave both switches open.

Demonstration Procedure:

1. Close both switches so the capacitor and inductor are not included.
2. Turn the radio on and tune to either a station or pink noise.
3. Observe that all frequencies are reaching the speaker.
4. Set the decade capacitor box to 10microfarads and throw the high pass switch to include the inductor.
5. Note that the low frequencies are reduced while the high frequencies still reach the speaker (high pass filter).
6. Switch the high pass filter back (no capacitor) and set the inductor to 6mH then throw the low pass switch to include the inductor.
7. Note that the high frequencies are reduced while the low frequencies still reach the speaker (low pass filter).
8. Next switch the high pass filter switch to include the capacitor.
9. Observe that only a small range of frequencies reach the speaker (band pass filter).
10. Explain that this is essentially how a 2-way speaker crossover works.

Note: Even when not tuned to a radio station, you may still here the local UMASS radio signal faintly.
This is because the signal is strong enough to be induced in either one of the components or the cables.
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