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 Year 12 Physics Tutorial 9.3.A – Forces on Conductors Module 9.3 – Motors and Generators Topic 9.3.A – Forces on Conductors Name Date Force on a Conductor in a Magnetic Field 1.
Show, on the following diagams, the direction of the magnetic field at each named point. 2.
The term “explain” means to relate cause and effect. (a) What is the cause of the ‘motor effect’? …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… (b) In the figure shown right, a current-­‐carrying conductor is in the field of a U-­‐shaped magnet. Show the direction of the force on the conductor. 3.
What is the direction of the force acting on each of the current-­‐carrying wires shown in figures (a-­‐d) shown below? A wire carrying an electric current is at right angles to a magnetic field. Predict what will happen to the force on this wire if the current is doubled. …………………………………………………………………………………………………………………………………………………………………………………………. 4.
The diagram below shows a conductor which is 50 cm in length carrying a current of 4.5 A, between the poles of two -­‐4
magnets. The flux density due to the magnets is 6.0 x 10 T. Find the force on the conductor. …………………………………………………………………………………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………………………………………………………………………………. Page 2 5.
Find the force on the conductor shown below when 2 A flows through it. ………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………… 6.
In the diagram, a horizontal magnetic field of strength 0.6 T is acting between the poles of a very strong magnet. A section of an electric circuit that is a straight wire passes at right angles through the magnetic field. The section of the wire that is in the magnetic field experiences a force of 1.2 N. (a) Predict the direction of the force. ……………………………………………………………………………………………………………….. (b) Calculate the length of the section of wire that is affected by the field. ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… 7.
Two conducting rails of negligible resistance are placed 50.0 cm apart as shown in the diagram. A conducting rod, also with negligible resistance, is placed across the rails. The mass of the rod is 100.0 g and there is negligible friction between the rod and rails. A 12.0 V battery is connected to the rails through a resistor. It is noticed that when a magnetic field of strength 0.3 T is applied at right angles to the incline, the rod slides down the frictionless -­‐2
rails at a constant acceleration of 0.15 ms . (a) Calculate the net force on the rod. …………………………………………………………………………………. ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… Page 3 (b) Calculate the current in the circuit. ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… (c) Calculate the resistance of the resistor. ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………… 8.
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Use the diagram on the right to answer the following questions. (a) Predict the direction of the magnetic field around the wires shown in the diagram. ……………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………… (b) A 7.0 cm length of wire experiences a force of 0.07 N when at right angles in a -­‐2
magnetic field of 3.0 x 10 T. Calculate the current that is flowing. ……………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………… The diagrams below show conductors in magnetic fields. (a) Predict the direction of the force on the wires in the diagram below. Page 4 (b) A wire at right angles through a magnetic field of strength 1.5 T carries a current of 0.07 A. If the wire experiences a force of 0.21 N, calculate the length of the section of wire in the magnetic field. ……………………………………………………………………………………………………………………………………………………….
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………………………………………………………………………………………………………………………………………………………. 10. A straight 3.0 cm long piece of copper wire of mass 0.06 g can just float horizontally in air because of the force of the a -­‐5
5.0 x 10 T horizontal magnetic field. (a) Identify the forces that are acting on the wire. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. (b) Calculate the current in the wire. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. 11. A current is flowing in a long conductor. An electronic device is being used to measure the strength of the magnetic field at distance d at right angles to the conductor. Predict what would happen to the strength of the magnetic field if: (a) the current in the conductor was tripled ……………………………………………………………………………………………………………………………………………………………………………………. (b) the distance from the conductor was halved ……………………………………………………………………………………………………………………………………………………………………………………. (c) the current in the conductor was halved and the distance quadrupled ……………………………………………………………………………………………………………………………………………………………………………………. Page 5 -­‐4
12. In the diagram below, a conductor of length 0.50 m is lying perpendicular to a magnetic field of flux density 4.5 x 10 T while carrying a current of 0.60 A towards the bottom of the page. (a) Determine the magnitude and direction of the force on the conductor. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. (b) Determine the magnitude and direction of the new force experienced by the conductor in part (a), if it was lying at o
an angle of X = 35 to the field lines as shown below. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. Page 6 Force Between Two Parallel Current Carrying Conductors 1.
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Two parallel wires, of length 5.5 cm are 0.15 cm apart, and currents of 1.0 A and 1.5 A, flow in the opposite direction to each other. Calculate the magnitude of the force between these wires. State the direction of this force. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. The two parallel current carrying conductors shown below carry currents of 1.5 A and 4.0 A. They are 20 cm apart in air and are 3.0m long. Calculate the force between the conductors. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. 3.
Calculate the force between the parallel sections of the wires shown. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. Page 7 4.
Compare the forces acting on the parallel sections of conductors 1 and 2 to (a) in the following situations. (a) (b) I 1= 1 A I 1= 2 A d = 10 cm d = 20 cm I = 1 A I = 2 A l = 1 m l = 1 m ……………………………………………………………………… ……………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… (c) (d) I 1= 1 A I 1= 0.5 A d = 5 cm d = 1 cm I = 5 A I = 2 A l = 2 m l = 10 m (e) ……………………………………………………………………… ……………………………………………………………………… I 1= 1 A (f) ………………………………………………………………………… ………………………………………………………………………… I 1= 10 A d = 25 cm d = 10 cm I = 0.5 A I = 0.5 A l = 250 m l = 2 m ……………………………………………………………………… ……………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… Page 8 5.
Determine the resultant force per unit length on Conductor 2 in the situation shown below. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………………………………………………………………. Page 9