What is magnetic force?
What is the magnetic force?
How to find the magnetic force?
Force on a wire
Figure 2: Magnetic force on a wire.
Figure 2 shows a wire running through the north and south poles of a horseshoe magnet. A battery is connected to the wire which causes a current of to flow through the wire in the direction shown. If the magnetic field between the poles is known to be , what is the magnitude and direction of the force on the section of wire between the poles?
Suppose the magnet was shifted a little to the left so that the wire is now closer to the south pole of the magnet. Would you expect any change in the force on the wire?
Suppose the strength of the magnet was not known. Can you suggest a way to modify this experiment to measure the strength of the magnetic field? Assume you have a ruler, string and some calibrated weights available.
Magnetic deflection of electrons in a cathode-ray tube
Figure 3 shows a cathode ray tube experiment. A pair of coils are placed outside a cathode ray tube and produce a uniform magnetic field across the tube (not shown). In response to the field, the electrons are deflected and follow a path which is a segment of a circle as shown in the figure. What is the direction of the magnetic field?
Figure 3: Cathode ray tube experiment.
If the electrons are known to be ejected from the electron gun horizontally at a speed of , what is the strength of the magnetic field? Assume that the radius of the circular path can be approximated by where is the length of the tube and is the horizontal deflection.