A-Level AQA Physics Work, Energy & Power: This question is about using a d

Question

This question is about using a digital balance to investigate the force on a wire placed in a magnetic field when there is an electric current in the wire.

A student carries out the procedure shown in Figure 1 and Figure 2.

A meter ruler is pushed into the 1.0 m mark and a prism is placed on a digital balance. The end of the ruler is raised and the balance is turned on and then set to zero, as shown in Figure 1.

The ruler’s then supported by the prism with the apex of the prism at the 30.0 cm mark as shown in Figure 2. The height of the prism is adjusted so that the ruler is horizontal.

1. Deduce the mass of the ruler. 
   State one assumption you make. 
   
   [3 marks]

2. The student attaches a current-carrying wire to the upper edge of the ruler, as shown in Figure 3. 
   The ends of the wire are connected to terminal blocks P and Q and are fixed firmly on the bench. A power supply and ammeter are connected between P and Q.

A horizontal uniform magnetic field is applied, perpendicular to the wire, between the terminal blocks.

The balance reading M is recorded for increasing values of current I. A graph of these data is shown in Figure 4.

3. State and explain the direction of the horizontal uniform magnetic field. 
   
   [2 marks]

4. It can be shown that $$B$$, the magnitude of the magnetic flux density of the horizontal uniform magnetic field, is given by $$B = \frac{F}{I l}$$ where: 
- F is the change in force acting on the prism per unit current in the wire 
- l is the length of the region where the magnetic field cuts through the wire.

Determine B. 
   
   [3 marks]

5. The experiment is repeated with the ruler pivoted at the 99.0 cm mark. Nothing else is changed from Figure 3. 
   This arrangement is shown in Figure 5.

Tick (✓) one box in row 3 or 4 of Table 1 to identify the effect, if any, on the magnitude of the forces acting on the apparatus as a certain current is passed through the wire.

Tick (✓) one box in row 3 or 4 of Table 1 to identify the graph produced for this modified experiment compared with the graph in Figure 4. 
   
   [3 marks]

6. Figure 6 shows the balance being used to measure the forces between two wires. 
   The connections joining these wires to the power supply are not shown. 
   The pair of the balance moves a negligible amount during use and it supports a straight conductor with wire X of horizontal length l.

A second conducting wire Y is firmly supported a distance above X.

Show, by adding detail to Figure 6, the wire connections that complete the circuit. 
   The currents in X and Y must have the same magnitude and be in the directions indicated. 
   
   [2 marks]

7. Explain what the student could do to find I.

This question is about using a digital balance to investigate the force on a wire placed in a magnetic field when there is an electric current in the wire - AQA - A-Level Physics - Question 1 - 2018 - Paper 3

Worked Solution & Example Answer:This question is about using a digital balance to investigate the force on a wire placed in a magnetic field when there is an electric current in the wire - AQA - A-Level Physics - Question 1 - 2018 - Paper 3

Deduce the mass of the ruler. State one assumption you make.

State and explain the direction of the horizontal uniform magnetic field.

Determine B.

Tick (✓) one box in row 3 or 4 of Table 1 to identify the effect, if any, on the magnitude of the forces acting on the apparatus.

Explain what the student could do to find I.

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