Self-Test: Electromagnetism (Forces) Test #1 
Suggested Time: 65 minutes
1. Which of the following diagrams best shows the magnetic field lines between the poles of two permanent magnets? 

2. A wire carrying 12 A of current is placed in a magnetic field of strength 0.63 T. 

What are the magnitude and direction of the magnetic force acting on the wire? 

3. A particle having a charge of 3.2 × 10 -19 C follows a circular path of 0.45 m radius while travelling at a speed of 1.2 × 10 4 m/s in a 0.78 T magnetic field. What is the mass of the particle? 
A. 7.8 × 10 -28 kg B. 9.4 × 10 -24 kg C. 1.1 × 10 -19 kg D. 3.0 × 10 -15 kg
4. Two particles Y and Z with equal mass and speed enter a uniform magnetic field and follow the paths as shown. How do their magnitude and polarity of charge compare? 

5. A wire carrying a current of 5.0 A is in a uniform 3.2 × 10 -2 T magnetic field as shown. What is the force on the 0.15 m length of wire? 
A. 0 N  B. 1.6 × 10 -2 C. 2.4 × 10 -2 D. 4.0 × 10 -2 N
6. An electron circulates in a uniform 5.0 × 10 -4 T magnetic field as shown. If the electron has 3.2 × 10 -18 J of kinetic energy, what is its radius of orbit, r
A. 2.3 × 10 -7 m B. 4.6 × 10 -4 m C. 2.5 × 10 -3 m D. 3.0 × 10 -2 m
7. A 5.0 A current flows through a 0.20 m long solenoid that contains 1500 loops. 

What are the magnitude and direction of the magnetic field at the centre of the solenoid? 

8. A coil has 680 turns of wire, a current of 5.6 A, and an area of 2.1 × 10 -2 m 2 . This coil is placed in a 0.22 T magnetic field in either field-coil orientation X or Y. 

Which field-coil orientation would produce a maximum torque, and what is the magnitude of this torque? 

9. A coil of area 0.32 m2 rotates in a 0.25 T magnetic field. When the current in the coil is exactly 4.8 A, the torque it produces is 55 N m. How many windings are there in the coil? 
A. 9 B. 21 C. 140 D. 3300
10. A compass placed on a table points north. In which direction should a conductor, placed directly above the compass, carry current in order to reverse the direction of the compass needle? 
A. east to west B. west to east
C. north to south D. south to north
11. The magnetic field around a current-carrying wire is investigated with a compass. 

At which of the four positions shown in the diagram will the compass needle point towards the bottom of the page? 

A. 1 B. 2 C. 3 D. 4
12. A beam of electrons is directed into a uniform magnetic field and deflects as shown in Figure I. If a beam of protons with the same speed were to enter this same magnetic field, which of the paths shown in Figure II would the protons take? 
A. 1 B. 2 C. 3 D. 4
13. A metal rod is resting on top of two 4.0 m long conducting rails that are separated by 1.8 m. The force of friction between the rod and the rails is 1.2 N. A magnetic field of 5.2 × 10 -2 T is directed upwards, as shown in the diagram below. 

How much current must be sent through the rod before the rod begins to move and in what direction will the rod move? 

14. Four identical pieces of wire are bent to form four different coils, each containing a different number of loops. Each coil carries 5.0 A of current and is placed in the same magnetic field of 0.2 T. Which of the four coils would experience the greatest maximum torque? 

15. A 35 loop square coil 0.12 m on a side is positioned in a 0.050 T magnetic field. A 0.20 kg mass is suspended from one side of the coil as shown in the diagram below. 

How much current must pass through the coil in order for the coil to remain horizontal? 
A. 2.3 A B. 4.7 A C. 9.3 A D. 330 A

16. With the electromagnet turned off, electrons in a cathode ray tube strike the centre of the screen as shown. 

When the electromagnet is turned on, where will the electron beam now strike the screen? 
A. 1 B. 2 C. 3 D. 4

17. The diagram below shows a current balance inside a long solenoid consisting of 525 turns. If the current I through the solenoid is 3.7 A and the current I through the balance is 4.5 A, what is the magnitude of the magnetic force on the balance? (diameter of solenoid 0.055m, length of solenoid 0.36 m, length of current balance inside the solenoid 0.18 m, width of current balance 0.035 m) (7 marks) 
18. A 0.400 m long solenoid has 6720 turns of wire. A current of 14.5 A flows in the solenoid. An electron inside the solenoid travels perpendicular to the axis of the solenoid with a speed of 6.50 × 10 5 m/s . What is the magnitude and direction (up, down, left , right) of the magnetic force acting on the electron? (7 marks) 
19. A 0.025 m wire segment is positioned in a 0.75 T magnetic field as shown in the diagram below. When a current is passed through this wire segment it experiences a 0.20 N force upwards. 

a) What is the direction of the current? From X to Y or from Y to X? (2 marks) 

b) What is the magnitude of the current? (5 marks)

20. An electron is accelerated from rest through a potential difference of 750 V. It then enters a uniform 2.3 × 10 -3 T magnetic field at right angles to the field. 

a) What is the speed of the electron? (3 marks) 

b) What is the radius of its path in the magnetic field? (4 marks)

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