$"1$ KHz $".$

$2.$ Now turn the power switches on for both the transmitter and the receiver. You can see the working indicators are on$.$ Adjust the amplifier knob on the receiver so that you can see the LED light. If you turn on the speaker switch, you should hear something.

$3.$ We can also use the vibrator receiver instead of the horn antenna to receive the electromagnetic wave. Connect the electromagnetic wave receiver and the vibrate receiver using the black wire, with one end connect to vibrate receiver, the other connect with the electromagnetic wave receiver by inserting it into the amplifier insert $($which reads $"$in$")$ as picture below. Adjust the direction of the horn antenna of the transmitter to make it point to the vibrate receiver instead of the antenna on the electromagnetic wave receiver.

$3\mathrm{.}2.$ Absorption of Electromagnetic Wave

$1.$ Adjust the amplifier knob on of the receiver so that $9$ of the $10$ LEDs have light on$.$

$2.$ Put the thinner wood block on the other one, standing on end. Push them slowly into the middle of the transmitter and the receiver. Watch the changes of the LED. Do some of the lights turn off, or the lights stay unchanged? Why? What's your

explaination?