PHYSICS STUDENT EXPERIMENT EXAMPLE
Rationale
Electromagnets are temporary magnets created by passing an electric current through a solenoid. When a charge is moving, a magnetic field is formed around it. The magnetic field created by the moving charge in a solenoid is focused in a uniform. direction, giving it the properties of a magnet.
An original experiment investigated the force exerted by an electric charge moving through a magnetic field, on the magnets creating the field. The magnetic field of moving charge (current) interacts with the magnetic field of the magnet creating a force perpendicular to the direction of the current and magnetic field. It was found that the force exerted by the charge is directly proportional to the rate of charge moving through (current).
Research into the phenomena found the force could be described by
Where I is current, L is length, B is the magnitude of the magnetic field (Cooper, 2012).
The relationship between current and the force exerted by the current on magnets lead to the question of the relationship between current and the force exerted by the current on an unmagnetised ferrous material.
Similarly, the magnetic field created by a current will interact with an unmagnetised ferrous material to create a force. In a piece of non-magnetised ferromagnetic material, the domains are randomly aligned; however, when an external magnetic field is applied, the magnetic domains align and the piece of metal will temporarily act as a magnet, creating a magnetic field (Nave, 2019).
Figure 1. diagram showing the effect of a magnetic field on unmagnetised ferromagnetic material Adapted from (Nave, 2019)
This magnetic field created by the ferrous material interacts with the original magnetic field of the moving charge creating a force. The interaction of this magnetic field with the magnetic field created by the current is weaker as the magnetisation of the ferrous material is lower (Clarke, 2010). Due to this consideration, a solenoid is used to focus the magnetic field of the current, creating a discernible impact on the force exerted.
Research has found that the force exerted by an electromagnet could be found by the formula:
Where F represents force, I is current, n is the numbers of loops in the solenoid, μ0 is the magnetic permeability of a vacuum, A is the area of the solenoid and g is the distance between the solenoid and the metal.
As such, this experiment modifies the original experiment by redirecting it towards investigating the relationship between the current of an electromagnet and the force it exerts.
If n, A and g are kept constant then the data should show a theoretical relationship of
Research question
What is the relationship between current in a solenoid and the force it exerts on unmagnetised ferromagnetic material (Iron) when solenoid density and distance to solenoid are constant?
Original Experiment
The original experiment investigated the force exerted by a charge moving through a wire in the magnetic field of a magnet at different currents (1A to 0.1A in 0.3A increments). Two trials were conducted at each current. No theoretical values were calculated as the magnitude of the magnetic field could not be found. As current increased, force exerted increased linearly.
Modifications
To collect sufficient, reliable and valid data, the methodology was:
• Redirected by
1. Measuring the force exerted by a moving charge in a solenoid on a nonmagnetic ferrous metal.
• Refined by
1. Maintaining a gap of 18cm between the top of solenoid and metal.
2. Measuring the force using a scale (±0.01g or ± 0.098N). A scale allows a precise measurement, improving the reliability of the data.
3. Using an ammeter (±0.01A) to measure current and rheostat to alter current, allowing trials to be conducted at precise intervals. This configuration gives greater control and precision of the current, improving reliability.
4. Using a ferrous material of iron which has a magnetic permeability of approximately 2000. The high permeability improves the validity of the experiment as it is closer to the theoretical assumption of permeability.
5. Measuring at five different currents (0.5, 1, 1.5, 2, 2.5A) to ensure that trends, patterns and relationships could be more easily identified, improving validity of findings.
6. Conducting five trials to ensure the reliability of the data.
• Extended by
1. Accounting for the distance and the properties of the solenoid in theoretical calculations. This improves validity as data could be compared.
2. Using a 700 loop, 11.3 cm2
solenoid to create a magnetic field that can exert a detectable force on the iron. A high number of loops and a greater area creates greater magnetic fields and thus a greater force which could be more easily observed and reduces uncertainty from instruments (same absolute but lower percentage uncertainty). This will, therefore, improve the reliability of the experiment.
Management of risk
To ensure the safety of the participant and address any ethical issues involved in the experiment, the following considerations were identified and addressed:
• The electricity used in the experiment may pose a hazard. This hazard could be mitigated by preventing contact with power points and open wires with electricity on. No water is to be brought within the laboratory.
• The magnetic field created by the solenoid may pose a risk to electronics. Maintain at least 1 meter between all electronics and the solenoids. Data is to be recorded on paper before transferred to digital media.
• The solenoid may overheat and pose dangers to participants. To avoid overheating, the solenoid is not to be on for prolonged periods and be allowed to rest for a minute between every trial.