Concept Quiz: Fields. Time: 15 minutes, then we’ll take it up!
1. Two exoplanets in orbit exert a gravitational force on other as shown. Which diagram
correctly shows the magnitude & direction of the forces involved?
2. Three masses (A, B, C) gravitationally attract one another. Between which pair is the
force the greatest?
a) AB
b) BC
c) AC
d) They’re all equal.
3. The Electric field at a point on a line between two charges, q1 and q2 is zero. What can
you conclude about the signs of q1 and q2?
a) Same sign
b) Opposite sign
c) it depends on where the point is zero
d) q1 and q2 must be neutral (not charged)
4. The field for an unknown object is shown. What type of field could this
diagram represent?
a) Gravitational
b) Electric
c) Magnetic
d) None of the above.
5. On an average day the Electric Field of the Earth’s atmosphere is directed downward.
What is the charge on the Earth?
a) Positive b) negative c) neutral
d) need more information.
⃑|=
6. Consider the two equations for an Electric Field: |𝐸
a)
b)
c)
d)
𝑘𝑞
𝑟2
𝐹
and |𝐸⃑ | = . What is the
𝑞
difference between them?
The first describes the “producer”, the second the “experiencer”.
Both can be used to calculate an Electric field strength in N/C.
They both have analogous gravitational field strength (𝑔) equations.
All the above are correct.
7. Which of the following Electric field diagrams are incorrect? Circle all that apply.
8. Is the ∆Ee (Electric potential energy) positive, negative, or zero for a H+ atom that moves
from 1 to 2 in the following?
a) Positive, negative
b) positive, negative c) negative, zero
d) zero, negative
9. What would be the ∆Ee for a neutral H atom in diagram 1 above?
a) Positive b) negative c) zero
10. Suppose you looked directly down the South pole of a bar magnet. The magnetic field
points
a) to the right
b) to the left
c) away from you
d) towards you
11. Suppose you wanted to deflect a +ve charge in an “S” path as shown,
using only magnetic fields. How could this be done using magnetic
fields perpendicular to the plane of the page?
How does the velocity out compare to the velocity in?
⃑ 𝑖𝑛 then 𝐵
⃑ 𝑜𝑢𝑡 of the page, velocity increased.
a) 𝐵
⃑ 𝑜𝑢𝑡 then 𝐵
⃑ 𝑖𝑛 the page, no change in velocity.
b) 𝐵
⃑ 𝑜𝑢𝑡 then 𝐵
⃑ 𝑖𝑛 the page, velocity increased.
c) 𝐵
⃑ 𝑖𝑛 then 𝐵
⃑ 𝑜𝑢𝑡 of the page, no change in velocity.
d) 𝐵
Answers:
1. C) equal & opposite forces
2. AC, FAB= 3F, FBC=3F, FAC=9F
3. A) Field vectors cancel
4. B) electric, as g is attractive, and B is parallel lines
5. B) negative, as direction of E shows how a +ve charge would move
6. D)
7. B, C, D, F since field lines do not cross, and are defined by the effect on a +ve test charge
8. Negative, zero
9. Zero (neutral objects unaffected by an E field)
10. C
11. d