Post Test: Electric and Magnetic Forces
Consider four objects: A, B, C, and D. If A is negatively charged and B and C attract A but repel each other, what is the charge on B and C?
A. Both B and C are positively charged.
Why does a glass rod become positively charged when it is rubbed with a silk cloth?
A. The electrons from the glass rod are transferred to the silk cloth.
How are magnetic poles and electrical charges similar?
A. Their same forces repel each other, and their opposite forces attract each other.
Why is a magnetic field a vector quantity?
A. directional force
One beam of electrons moves at right angles to a magnetic field. The force on these electrons is 4.9 × 10-14 newtons. A second beam travels at the same speed, but at a 30° angle with the magnetic field. What force is on these electrons?
B. (4.9 × 10-14 newtons) · sin(30°)
The electric force between two charged vinyl balloons is 3.0 × 10-3 newtons. If the distance between them is 6.0 × 10-2 meters and the charge of one vinyl balloon is 3.3 × 10-8 coulombs, what is the charge on the other vinyl balloon? (k = 9.0 × 109 newton·meter2/coulombs2)
B. 3.6 × 10-8 coulombs
What is the difference between the fields surrounding a stationary charge and those that surround a moving charge?
B. A moving charge has both an electric and magnetic field and a stationary charge has only an electric field.
What is the direction of magnetic field lines inside any magnet?
B. They travel from south to north.
If you wanted to increase the voltage, which would you use?
B. step-up transformer
A positive charge is moving from the floor of a room toward the ceiling. A magnetic field runs from east to west. In what direction is the magnetic force on the moving positive charge?
B. toward the south
When is the magnetic field the strongest?
B. when the field lines are close together
What is the magnetic force acting on an electron if its speed is 3.0 × 106 meters/second and the direction is perpendicular to a magnetic field of 0.020 teslas? The value of q = -1.6 × 10-19 coulombs.
C. F = -9.6 × 10-15 newtons
What happens when a negatively charged object A is brought near a neutral object B?
C. Object B stays neutral but becomes polarized.
What happens to an electric current produced from an electromagnet when the direction of the magnetic field changes?
C. The direction of the electric current changes.
Which statement is true about a polarized object?
C. The number of positive and negative charges can be the same.
Which situation would create a field like the one shown here?
C. an interaction between a magnetic south pole and a north pole
What is the emf produced in a 1.5 meter wire moving at a speed of 6.2 meters/second perpendicular to a magnetic field of strength 3.96 × 10-3 newtons/amp·meter ?
E. 0.037 volts
The electric force between a charged foam cup and a positively charged metal sphere is 2.12 newtons. If the charge on the cup is 2.0 × 10-6 coulombs and the charge on the metal sphere is 2.5 × 10-6 coulombs, what is the distance between the two? (k = 9.0 × 109 newton·meter2/coulombs2)
E. 1.5 × 10-1 meters
A proton travels at right angles through a magnetic field of 0.025 teslas. If the magnitude of the magnetic force on the proton is 1.8 × 10-14 newtons, what is the velocity of the proton? The value of q = 1.6 × 10-19 coulombs.
E. 4.5 × 106 meters/ second
Two balloons having the same charge of 1.2 × 10-6 coulombs each are kept 5.0 × 10-1 meters apart. What is the magnitude of the repulsive force between them? (k = 9.0 × 109 newton·meter2/coulombs2)
E. 5.2 × 10-2 newtons
Which of the following actions cannot induce voltage in a wire?
E. moving a wire parallel to a magnetic field
A wire that is 0.36 meters long moves perpendicularly through a magnetic field at a speed of 0.21 meters/second. The induced emf produced in the wire is 0.45 volts. What is the magnetic field strength?
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Which statement best explains the relationship between the electric force between two charged objects and the distance between them?
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