Magnetic Fields and Forces

Units of a magnetic field might be: 

• C×m/s 
• C×s/m 
• C/kg
• kg/C×s 

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The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is: 

• one of the directions of the velocity when the magnetic force is zero 
• the direction of the velocity when the magnetic force is a maximum 
• the direction of the magnetic force 
• perpendicular to the velocity when the magnetic force is zero 

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NGSS.HS-PS3-5

An electron is moving north in a region where the magnetic field is south. The magnetic force exerted on the electron is: 

• zero 
• up
• north
• south 

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A magnetic field exerts a force on a charged particle:

• always 
• never 
• if the particle is moving across the field lines
• if the particle is moving along the field lines 

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A proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. The ratio of their speeds, v_proton/v_alpha is: 

• 0.5 
• 1
• 2
• 4

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NGSS.HS-PS2-5

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An electron travels due north through a vacuum in a region of uniform magnetic field  that is also directed due north. It will: 

• be unaffected by the field 
• speed up
• slow down
• follow a right-handed corkscrew path 

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An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field. They experience magnetic forces, which are initially: 

• identical
• equal in magnitude but opposite in direction 
• in the same direction and differing in magnitude by a factor of 1840 
• in opposite directions and differing in magnitude by a factor of 1840 

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A beam of electrons is sent horizontally down the axis of a tube to strike a fluorescent screen at the end of the tube. On the way, the electrons encounter a magnetic field directed vertically downward. The spot on the screen will therefore be deflected: 

• upward
• downward 
• to the right as seen from the electron source 
• to the left as seen from the electron source 

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NGSS.HS-PS2-5

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An electron (charge = –1.6 ´ 10^–19 C) is moving at 3.0 ´ 10⁵ m/s in the positive x direction. A magnetic field of 0.80 T is in the positive z direction. The magnetic force on the electron is: 

• 0 N
• 4.5 ´ 10^–14 N in the positive z direction
• 4.5 ´ 10^–14 N in the negative z direction 
• 4.5 ´ 10^–14 N in the positive y direction 

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NGSS.HS-PS2-5

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