Question 145
Making an air cooler. You need an old towel, a frame to hang it, a tray long enough to hold one edge of the towel, water, a desktop fan, a thermometer and stand.
Safety: keep water away from electric cables, wall sockets and the fan. Keep the fan as far from the wall socket as possible. Make sure the fan can be switched off at the socket immediately if water spills. Only operate switches with dry hands.
1 Make sure the thermometer is dry; clamp it in a stand for all air temperature measurements.
2 Measure the temperature of the air in the room.
3 Switch the fan on and measure the temperature of air coming from the fan.
4 Soak the towel in water and hang it on the frame.
5 Fill the tray with water and position the towel with its bottom edge in the water.
6 Move the fan to about 10 cm from the wet towel and switch it on, blowing at the towel.
7 Measure the temperature of the air between the fan and the wet towel.
Explain any other differences that you would predict if a dry towel were used in place of the wet towel.
Safety: keep water away from electric cables, wall sockets and the fan. Keep the fan as far from the wall socket as possible. Make sure the fan can be switched off at the socket immediately if water spills. Only operate switches with dry hands.
1 Make sure the thermometer is dry; clamp it in a stand for all air temperature measurements.
2 Measure the temperature of the air in the room.
3 Switch the fan on and measure the temperature of air coming from the fan.
4 Soak the towel in water and hang it on the frame.
5 Fill the tray with water and position the towel with its bottom edge in the water.
6 Move the fan to about 10 cm from the wet towel and switch it on, blowing at the towel.
7 Measure the temperature of the air between the fan and the wet towel.
Explain any other differences that you would predict if a dry towel were used in place of the wet towel.
