4.5.3. Magnetic effect of a current
A subsection of Physics, 5054, through 4. Electricity and magnetism
Listing 10 of 29 questions
shows the coil of a loudspeaker attached to a cardboard cone. One pole of a stationary cylindrical magnet lies near to the coil. cylindrical magnet cardboard cone 60 Hz a.c. supply coil N S There is an alternating current in the coil of the loudspeaker. A student hears the note produced. Explain why the cone of the loudspeaker vibrates. Explain how the vibrating cone produces sound waves in the air. A stronger cylindrical magnet is now used. State the difference in the note heard.
5054_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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shows a solenoid made from wire wound around a plastic cylinder. plastic cylinder + – A current in the solenoid produces a magnetic field. On , draw the pattern of the magnetic field lines inside and outside the cylinder. shows a beam of beta-particles, in a vacuum, passing into a magnetic field. magnetic field out of the page beta-particles The movement of the beta-particles from left to right is an electric current. On , draw an arrow to show the direction of the conventional current. A solenoid is used to produce the magnetic field that lies within the shaded region of . The direction of the field is out of the page. 1. On , draw the path followed by one of the beta-particles in the shaded region. 2. The direction of the current in the solenoid is reversed. State what happens to the path of the beta-particle.
5054_w12_qp_21
THEORY
2012
Paper 2, Variant 1
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11 A wire is wound around a soft-iron core forming a solenoid, as shown in . variable resistor 12 V battery solenoid gap core There is a gap in the core. The solenoid is connected in series with a 12 V battery and a variable resistor . The resistance of the solenoid is 0.30 Ω and the variable resistor is set so that it has a resistance of 4.5 Ω. Calculate the current in the solenoid. current = The current in the solenoid magnetises the soft-iron core. Explain how the electric circuit is used to increase the strength of the magnetic field. shows a horizontal, current-carrying wire PQ in the gap. gap core P Q 1. The magnetic field in the gap is uniform and vertically upwards. The current in PQ is from left to right. Describe the effect of the magnetic field on PQ. 2. State the effect on PQ of increasing the strength of the magnetic field in the gap. The starter motor in a car is powered by a 12 V battery that is positioned next to the motor. The current in the motor is 75 A. Calculate the power supplied by the battery. power = Suggest and explain why the wires that connect the motor to the battery are very thick. A relay is used to switch on a starter motor in a car. Describe how the relay works. You may include a diagram in your answer.
5054_w12_qp_22
THEORY
2012
Paper 2, Variant 2
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A straight length of copper wire lies horizontally between the poles of a U-shaped magnet. shows the two ends of the wire connected to a very sensitive, centre-zero ammeter. sensitive, centre-zero ammeter S N copper wire The copper wire is moved upwards slowly between the two magnetic poles. The needle on the ammeter deflects to the right. Explain why the needle on the ammeter deflects. The wire is moved downwards very quickly between the two magnetic poles. State what happens to the needle on the ammeter. State what happens to the needle on the ammeter when the copper wire is moved horizontally between the two poles.
5054_w14_qp_21
THEORY
2014
Paper 2, Variant 1
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Thin wire, covered in plastic insulation, is used to make a solenoid (long coil). The solenoid is connected to a sensitive ammeter. shows the N-pole of a steel magnet placed next to the solenoid. A solenoid steel magnet X Y N Point X and point Y are on the axis of the solenoid. Explain why plastic is an electrical insulator. Explain why the magnet is not made from 1. aluminium, 2. iron. In one experiment, the magnet in is moved to the left and passes into the solenoid. The N-pole of the magnet travels from Y to X at a constant speed. As it moves, the ammeter shows a small current. Explain why there is a current in the solenoid when the magnet is moving. The N-pole travels from Y to X in 0.14 s. As it moves, the current shown on the ammeter is 0.045 mA. The resistance of the solenoid is 1.2 Ω. Calculate 1. the potential difference (p.d.) across the solenoid, potential difference = 2. the charge that passes through the solenoid as the N-pole moves from Y to X. charge = In a second experiment, the speed of the N-pole is greater than its speed in the first experiment. It now takes only 0.070 s to travel from Y to X. A current in the same direction is shown on the ammeter. State and explain how the size of this current compares with the size of the current in the first experiment. The same quantity of charge passes through the coil in both the first and second experiments. Explain why this is the case. State two ways in which the equipment shown in can be used to produce a current in the solenoid that is in the opposite direction. 1. 2.
5054_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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In a cathode-ray oscilloscope (c.r.o.), a beam of electrons is produced by a filament at one end of an evacuated glass tube. The electrons are then accelerated and strike a screen at the other end of the tube. Describe how the electrons are produced by the filament and how they are then accelerated. Explain why the glass tube is evacuated. The instruction booklet for a c.r.o. states that strong magnets must not be placed close to the c.r.o. Explain why a strong magnet close to the c.r.o. deflects the electron beam.
5054_w16_qp_22
THEORY
2016
Paper 2, Variant 2
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A vertical solenoid (long coil) with an iron core is held in a wooden clamp above a laboratory bench. The solenoid is connected in series with a battery, a switch S, an ammeter and a variable resistor. There is a voltmeter in parallel with the solenoid. represents this apparatus. V A S battery iron core solenoid A student closes switch S and a current in the circuit produces a reading on the ammeter. State what is meant by current. The battery consists of five 1.5 V cells in series. The reading on the ammeter is 4.0 A. State the size of the electromotive force (e.m.f.) of the battery. Calculate the total resistance of the series circuit. resistance = The reading on the voltmeter is 6.5 V. Calculate the power dissipated in the solenoid. power = The solenoid is made of copper and the student notices that, as time passes, the solenoid becomes extremely warm. State and explain the effect of this temperature increase on the ammeter reading. The current in the solenoid magnetises the iron core so that the lower end of the core is an N-pole. On , draw the pattern and indicate the direction of the magnetic field in the region surrounding the iron core. The student holds an iron cylinder against the bottom surface of the iron core in the solenoid. When he releases the iron cylinder, it stays in contact with the iron core. 1. Explain why the iron cylinder does not fall. 2. The switch S is opened. State and explain whether the iron cylinder remains in contact with the iron core.
5054_w16_qp_22
THEORY
2016
Paper 2, Variant 2
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An electromagnet is used to separate objects that are magnetic from objects that are non-magnetic. shows the electromagnet suspended from the arm of a crane. electromagnet crane electric cable State the name of the metal from which the core of the electromagnet is made. The electromagnet is powered by a 220 V d.c. (direct current) supply. The electromagnet is switched on and the current in the circuit is 39 A. Calculate the power transferred to the electromagnet. power = The d.c. supply is a set of batteries. The batteries power the magnet for 4.5 hours before they need to be replaced. Calculate the charge driven around the complete circuit in this time. charge = On a very cold morning, when the electromagnet is first switched on, the current is greater than 39 A before decreasing to the usual value. Explain why the current is initially greater than 39 A.
5054_w22_qp_21
THEORY
2022
Paper 2, Variant 1
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Questions Discovered
29