Topic 6 Fields and Forces Name:

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Topic 6 Fields and Forces Name:





1.

An isolated metal sphere of radius 50.0 cm has a positive charge. On the diagram below
,

draw lines to
represent the electric field outside the sphere.







(2)










2.

(a)

Using the diagram below, draw the magnetic field pattern of the Earth.



(2)









(
b)

State
an

object
that
produces a magnetic field pattern similar to that of the Earth.


(1)


.............................................................................................................................
......


(c)

A

vertical
wire passes through a sheet of cardboard that is held horizontally. A small compass is placed at
the point P and the needle points in the direction shown.

A current is passed through the wire and the
compass needle now points in a direction that makes an a
ngle of 30
º

to its original direction
.






(i)
Draw a
n arrow on the wire to show the
direction of current in the wire. Explain why it is in the direction that
you have drawn.










(2)


................................................................
.....................................................................................................

.............................................................................................................................
.............................
............

.............................................................................................................................
.........................................


(ii)

The magnetic field strength at point P due to the current in the wire
is
B
W

and the strength of the
horizontal component of the Earth’s magnetic field is
B
E
.

Deduce, by drawing a suitable vector diagram,
that

B
E

=
B
W

tan 60
º
.








(2)





2


3.

A proton may be considered to be a point charge. For such a proton

(i)

C
alculate th
e magnitude of the electric field strength at a distance of 5.0 × 10

11

m from the proton.


(2)


.............................................................................................................................
..................................
.....

.............................................................................................................................
.......................................

.....................................................................................
...............................................................................

(ii)

In a simple model of the hydrogen atom, an electron orbits the proton. Both electron and proton are regarded as
point charges. The orbital radius of the electron is 5.0 x
10

11

m
.
Using your answer to (i), deduce that the
magnitude of the electric force between the electron and the proton is 9.3 × 10

8
N.



(2)


..................................................................................................................
..................................................

.............................................................................................................................
.......................................

........................................
............................................................................................................................


4.

(
a)

Electric fields and magnetic fields may be represented by lines of force. The diagram below shows
some lines of force

.



(i)

State whether the field strength at A and at B is constant, increasing or decreasing when measured in the
direction from A towards B.




at A: ...............................................at B: .....................
............................


(2)


(ii)

Explain why field lines can never touch or cross.







(2)


.............................................................................................................................
.......................................

.........................
.............................................................................................................................
..............

....................................................................................................................
................................................


(b)

A bubble chamber is used to show the paths of particles. A high
-
energy particle enters the chamber and, at a
point P, there is a reaction that gives rise to two charged particles. The tracks of the part
icles are shown below.



There is a uniform field of force acting normally to the plane of the paper.

(i)

State, and explain, whether the field of force is electric or magnetic.




(2)


.....................................................................
...............................................................................................

.............................................................................................................................
...................................
....

.............................................................................................................................
.......................................


(ii)

The path of each of the two particles produced in the reaction is a spiral. One
particle is spiralling
clockwise, the other anti
-
clockwise. Suggest why they spiral in opposite directions.


(1)



3

.............................................................................................................................
.................
......................

5.

This question is about gravitational fields.

(a)

Define
gravitational field strength
.







(2)


.............................................................................................................................
........
...............................

.............................................................................................................................
.......................................

...........................................................
.........................................................................................................


(b)

The gravitational field strength at the surface of Jupiter is 25 N kg

1

and the radius of Jupiter is
7.1
x

10
7

m.

(i)

Derive an expression for th
e gravitational field strength at the surface of a planet in terms of its
mass
M
, its radius
R

and the gravitational constant
G
.


.............................................................................................................................
.
......................................

.............................................................................................................................
.......................................

....................................................
................................................................................................................

(2)

(ii)

Use your expression in (b)

(i) above to estimate the mass of Jupiter.



(2)


.........................................................
...........................................................................................................

.............................................................................................................................
.......................
................

.............................................................................................................................
.......................................


6.

(i) A wire carries a current of 30 A and 12 cm of the wire are in a ma
gnetic field of 0.90T at 60

. Calculate the force
on the wire








(2)








(ii) Calculate the magnitude of the magnetic field if a proton moving at 5.0 x 10
6

ms
-
1

feels a force of 8.0 x 10
-
14

N
(2)