Physics and Astronomy Outreach Program at the University of British Columbia

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Multiple-Choice Questions

Electricity Generation

Generating Electricity


Question 1If the wire was moved in the directionof the arrow, what would happen to the charges in the wire?


A. +ve charges pushed to a, -ve charges pushed to b.

B. +ve charges pushed to b, -ve charges pushed to a.

C. +ve charges pushed to c, -ve charges pushed to d.

D. +ve charges pushed to d, -ve charges pushed to c.

E. Nothing

Uniform B field (pointing into the page)

va

dc

b


Question 1 AnswerIf the wire was moved in the directionof the arrow, what would happen to the charges in the wire?






E. Nothing


va

dc

b


Question 1 ExplanationElectricity

Generation


va

dc

b

Here, we see that the velocity is perpendicular to the magnetic field. We know therefore, that there will be a force that pushes the –ve charges in a direction perpendicular to BOTH the velocity AND the magnetic field – either toward a or toward b. To determine which of the two directions, use the right hand rule point your fingers in the direction of the field (into the page), face your palm in the direction of the velocity (to the left) and your thumb will point in the direction of motion of the –ve charges : toward a.








E. Nothing


va

d

cb



Generation


va

d

cb

Here, we see that the velocity is perpendicular to the magnetic field. We know therefore, that there will be a force that pushes the –ve charges in a direction perpendicular to BOTH the velocity AND the magnetic field – either toward a or toward b. To determine which of the two directions, use the right hand rule point your fingers in the direction of the field (into the page), face your palm in the direction of the velocity (to the left) and your thumb will point in the direction of motion of the –ve charges : toward a.








E. Nothing

Uniform B field (pointing OUT OF the page)

va

dc

b








E. Nothing


va

dc

b



Generation


va

dc

b

Here, we see that the velocity is perpendicular to the magnetic field. We know therefore, that there will be a force that pushes the –ve charges in a direction perpendicular to BOTH the velocity AND the magnetic field – either toward a or toward b. To determine which of the two directions, use the right hand rule: point your fingers in the direction of the field (into the page), face your palm in the direction of the velocity (to the left) and your thumb will point in the direction of motion of the –ve charges : toward b.


Question 4Which of the following will NOT light upthe bulb?


A. Option AB. Option BC. Option CD. Option D.


Question 4 AnswerWhich of the following will NOT light upthe bulb?





Generation

In situation C, the wires are moving but the + charges in each wire will be pushed outward (radially), so no electricity will flow around the loop.

In situation D, all the charges in the top half will be pushed down, and all the charges in the bottom half will be pushed up. These pushes will just cancel out, and again nothing will flow around the loop.


Question 5Which of these will light the bulbmost strongly?




Question 5 SolutionWhich of these will light the bulbmost strongly?





Generation

Situation B will light the bulb most strongly:We get the best results when one side of the loop is in a field Upwards, and the other side is in a field Downwards. This way the pushes on the charges push in the same direction AROUND the loop.


More Information: The right hand rule


More information on the right hand rule used to answer the previous questions can be found on the Hypherphysics site:

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html

Physics and Astronomy Outreach Program at the University of British Columbia

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