PHYS110-How Things Work

Notes on Speakers Lab

Coil & Oscilloscope
When the coil was connected to the oscilloscope and a magnet was moved near the coil, you should have seen the line on the scope move (but only move when the magnet or coil was moved). The oscilloscope measure voltage. Since voltage is related to current, the fact that the display moved means that the coil had current.

Hanging Coil The coil was hung by a wire that connected the two ends. Thus the coil was part of a complete circuit. (In the first part of the lab, the oscilloscope helped form a complete cicuit.) As the magnet is moved near the coil, again current is induced in the coil. Since there is current in the coil, the coil will have its own magnetic field. Both the cow magnet and the coil are thus both magnets and will attract or repel based on how the fields are aligned. In this case the current induced in the coil by the magnet will produce a magnetic field in the coil that will act to oppose the motion of the magnet. Thus as the magnet is brought near, the coil will repel away. As the magnet is pulled away, the coil will attract the magnet.

Battery and Switch
When the coil is connected to a switch and battery, current is produced when the switch is closed, thus forming an electromagnet. The electromagnet will be attracted or repelled to the cow magnet depending on how the two are aligned.

Signal Generator
Next the coil is connected to the signal generator by way of a "T" connector. The T connector simply allows you to view the signal coming from the signal generator. The signal generator creates an oscillating current in the coil. This means the coil will also have a changing magnetic field. If the cow magnet is brought near the coil the two will be attracted or repelled depending on the current at any instant. Since the current is changing, the coil and magnet will vibrate (since they are attracted and repelled). By placing the coil on the table, the vibrating coil then makes table vibrate. The vibrations can then be heard by placing your ear against the table. Thus the table amplifies the vibrations of the coil.

Sound is the vibration of gas liquid or solids. So, the signal generator causes the ciol to vibrate, which thus generates sound and the table amplifies these sounds.

CD Player
Finally, instead of using the signal generator, the coil is connected to the CD player. The electronic signal from the boom box put a chaning current in the coil. As with the signal generator, a changin current is created in the coil. This means the coil will also have a changing magnetic field. If the cow magnet is brought near the coil the two will be attracted or repelled depending on the current at any instant. Since the current is changing, the coil and magnet will vibrate (since they are attracted and repelled). Next the coil is taped to a piece of manila folder, making it vibrated as well. Since the larger folder can move more air than just the coil, more sound is heard.