Activity 1. Magnetic field in the coil cavity
- Before proceeding with your tasks, recall the main characteristics and differences between classical bar magnets and electromagnets.
|
PERMANENT MAGNET |
ELECTROMAGNET |
| Creates its magnetic field without an external power source | The magnetic field is created by an electric current |
| Its magnetic field is constant | It creates a magnetic field only when an electric current passes through it |
| Its magnetic poles cannot change | Its magnetic poles depend on the direction of current flow |
| Its magnetic field is of constant strength | The strength of its magnetic field depends on the magnitude of the electric current passing through it |
| Cannot be excluded | Can be switched on and off |
- Familiarise yourself with the specifics of the winding (coil).
If we wrap a wire around a core, usually cylindrical, we have coil. The long and thin coil is called a solenoid.
Solenoid. Source: https://st2.depositphotos.com/13282202/42654/i/1600/depositphotos_426546296-stock-photo-set-solenoid-coils-black-ferrite.jpg
If an electric current passes through the coil, a magnetic field is created in and around the coil and its cavity. The strength and direction of the magnetic field at a given point in space can be expressed in terms of magnetic induction. It is denoted by the letter B and has the unit Tesla (T). The tesla is a relatively large unit, so in practice, the thousand times smaller unit, the millesla (mT), is used.
The strength and direction of the magnetic field in the coil cavity can be measured with a tensiometer. The measured results depend on various factors, especially the magnitude of the current flowing through the coil.
If we place a core of magnetically soft steel in a coil through which current flows, we get an electromagnet. It has its poles and attracts iron objects.
- Study the information from the text and diagram.
Rita and Martin experimented to investigate the strength of the magnetic field in the cavity of a solenoid. They record the measured values in a table and present them in a diagram. The blue line reflects the first measurement, where the electric current only passed through 200 turns of the coil. The red line reflects the second measurement where the electric current has passed through 400 turns of the coil.
- Solve the problems using the previous information.
4.1. Transfer the values from the diagram to the given table.
|
|
I (A) | 0.5 | 0.75 | 1.0 | 1.25 | 1.5 | 1.75 |
2.0 |
|
N1 = 200 |
B (mT) |
|||||||
|
N2 = 400 |
B (mT) |
4.2. Answer the questions:
- Does the strength of the coil’s magnetic field depend on the number of turns on the coil? How?
- Does the strength of the coil’s magnetic field depend on the magnitude of the current in the coil windings?
- Complete the sentence: The strength of the electromagnet’s magnetic field is increased by …………. and by ………………
To download: Worksheet 1. Magnetic field in the coil cavity
