Formative test on principles of electromagnetism, including Lorentz force, Faraday's law, Lenz's Law, DC motors, AC generators and transformers.
Required
3 points
3
Question 1
1.
The output of a device is shown.
Which diagram(s) represent the device that has the output shown? Note: More than one answer may be correct.
Required
1 point
1
Question 2
2.
An electron travelling in a straight line with an initial velocity, u, enters a region between two charged plates in which there is an electric field causing it to travel along the path as shown.
A magnetic field is then applied causing a second electron with the same initial velocity to pass through undeflected. Which row of the table shows the directions of the electric and magnetic fields when the second electron enters the region between the plates?
1 point
1
Question 3
3.
Two parallel wires, X and Y, each carry a current I.
The magnitude and direction of the force on wire Y are represented by the vector F. The current in wire Y is then doubled and its direction is reversed. The current in wire X remains unchanged. Which vector arrow represents the force on wire X after the change to the current in wire Y?
1 point
1
Question 4
4.
A conductor PQ is in a uniform magnetic field. The conductor rotates around the end P at a constant angular velocity.
Which graph shows the induced emf between P and Q as the conductor completes one revolution from the position shown?
1 point
1
Question 5
5.
A positively charged particle is moving at velocity, v, in an electric field as shown
What is the direction of the force acting on the particle due to the electric field?
1 point
1
Question 6
6.
Which graph shows the magnitude of back emf induced in a DC motor rotating continuously as the rotational frequency increases.
1 point
1
Question 7
7.
Two long, parallel conductors X and Y are connected to a light bulb and an AC power supply. The conductors are suspended horizontally from fixed points using sensitive spring balances. X is positioned directly below Y.
3 points
3
Question 8
8.
A DC motor is rotated with a period of 0.2 s. On the axes below, sketch how the induced emf varies against time. Note: only the time axis requires a scale. You should assume that it starts rotation at the position shown.
Required
5 points
5
Question 9
9.
Watch the video below. Describe your observations and explain them with reference to appropriate Physics concepts.
Required
1 point
1
Question 10
10.
A DC motor is constructed from a single loop of wire with dimensions 0.10 m × 0.07 m. The magnetic field strength is 0.40 T and a current of 14 A flows through the loop.
Required
1 point
1
Question 11
11.
A stationary coil of 35 turns and cross-sectional area of 0.02 m2 is placed between two electromagnets and connected to a voltmeter as shown. The electromagnets produce a uniform magnetic field of 0.15 T through the coil.
The magnitude of the magnetic field is then reduced to zero at a constant rate over a period of 0.4 s. Calculate the magnitude of the emf induced in the coil. Marks will be awarded for working if your numerical answer is incorrect.
4 points
4
Question 12
12.
Two identical solenoids are mounted on carts as shown. Each solenoid is connected to a galvanometer, and the solenoid on cart 1 is also connected to an open switch and a battery. The total mass of cart 1 is twice that of cart 2.
Explain what would be observed when the switch on cart 1 is closed. In your answer, refer to the current in each galvanometer and the initial movement of the carts.
Required
1 point
1
Question 13
13.
A bar magnet is moved away from a stationary coil. Which diagram correctly shows the direction of the induced current in the coil and the resulting magnetic polarity of the coil?
1 point
1
Question 14
14.
A circular loop of wire is connected to a battery and a lamp. The apparatus is moved from P to Q along the path shown at a constant velocity through a region containing a uniform magnetic field.
Which graph shows the brightness of the lamp as the apparatus moves between P and Q?
1 point
1
Question 15
15.
The diagram shows a current-carrying conductor in a magnetic field.'
1 point
1
Question 16
16.
The diagram shows some parts of a simple DC motor.
Which row of the table correctly describes the direction of force acting on side WX and the direction of torque this produces on the coil?
1 point
1
Question 17
17.
The diagram shows a DC circuit containing a transformer.
The potential differences V1 and V2 are measured continuously for 4 s. The switch is initially closed. At t = 2 s, the switch is opened. Which pair of graphs shows how the potential differences V1 and V2 vary with time over the 4-second interval?
1 point
1
Question 18
18.
A magnet rests on an electronic balance. A rigid copper rod runs horizontally through the magnet, at right angles to the magnetic field. The rod is anchored so that it cannot move.
Which expression can be used to calculate the balance reading when the switch is closed?
1 point
1
Question 19
19.
A magnet approaches a coil with six turns, as shown in the diagram below. During time interval ∆t, the magnetic flux changes by 0.05 Wb and the average induced EMF is 1.2 V.
Which one of the following is closest to the time interval ∆t?
1 point
1
Question 20
20.
Transformers are equally capable of changing the voltage of a.c. and d.c. sources
1 point
1
Question 21
21.
1 point
1
Question 22
22.
A student builds a model electric generator, similar to that shown in the diagram below.
The coil consists of 50 turns of wire and has an area of 6.0 x 10 - 3 m2. The magnetic field between the poles of the magnets is measured to be 0.15 T.
What is the flux linkage in the loop?
1 point
1
Question 23
23.
A student builds a model electric generator, similar to that shown in the diagram below.
The coil consists of 50 turns of wire and has an area of 6.0 x 10 - 3 m2. The magnetic field between the poles of the magnets is measured to be 0.15 T.
The student rotates the coil in the direction indicated on the diagram. The coil is rotated a quarter turn (90o) in 23 ms.
What is the RMS voltage induced by the generator?
1 point
1
Question 24
24.
A rectangular coil of wire is placed in a uniform magnetic field B that is directed out of the page. This is shown below. At the instant shown the coil is parallel to the page.
The coil rotates about the axis XY. The time variation of the voltage induced between points P and Q is shown in the diagram below.
Which of the graphs below shows the variation of voltage versus time if the coil is rotated at twice the original speed?
1 point
1
Question 25
25.
An array of wind turbines is used to generate electrical power for an isolated community. The turbines are located 5.0 km from the community.
,
The transmission lines have a total resistance of 0.5 W. On a particular occasion the power produced is 24 kW at a RMS voltage of 240 V.
What power is ‘lost’ in the transmission lines.
1 point
1
Question 26
26.
An ideal transformer is designed to give a 6.0 V output from a 240 V input. The primary coil consists of 1000 turns. Which row of the following table is correct?