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SPH 4U
1.
Gravitational, Electric & Magnetic Fields Review
How much energy would it take to put a 4.00 x 104 kg space shuttle into an orbit 584 km above
the surface of the Earth to fix the Hubble telescope from rest on the surface?(1.36 x 10 12 J)
RE = 6.38 x 106 m
mE = 5.98 x 1024 kg
G = 6.67 x 10-11 Nm2/kg2
2. a) How much work does it take to put a 500 kg communications satellite in an orbit 1.0 x 10 3 km
above the surface of the Earth from the surface of the Earth?
b) As the satellite moves from this orbit to an orbit 3.0 x 103 km above the surface, what are
the changes in kinetic and potential energies?
c) What is the binding energy in this second orbit?
(1.77 x 1010 J, Ek = 2.88 x 109 J, Epg = 5.75 x 109 J)
3.
Assume that an electron is in a near circular orbit, radius 1.6 x 1010 m, about a helium nucleus:
a)
What is the electric field at the position of the electron?
(1.13 x 1011 N/C)
b)
What is the electric force on the electron?
(1.81 x 108 N)
c)
What is the electric potential at the position of the electron? (18 V)
4.
In an experiment, two small conducting spheres (0.500 g each) were suspended on two fine
insulating fibres 75.0 cm long. When equal charges were placed on the two spheres, they
separated and came to rest with a distance of 8.80 cm between centres. What was the
amount of charge on each sphere?
(1.57 x 108 C)
5.
A 1.0 x 10-6 C test charge is 40 cm from a 3.2 x 10-3 C charged sphere. How much work was
required to move it there from a point 100 cm away from the sphere? (43 J)
6.
Two alpha particles (mass = 6.6 x 10-27 kg, charge = 3.2 x 10-19 C), separated by an enormous
distance, approach each other along a "head-on collision" path. Each particle has a speed of
3.0 x 106 m/s to begin with. Calculate their minimum separation assuming no deflection from
their original path. (1.6 x 10-14 m)
7.
Determine the electric potential and electric field intensity at a point 0.40 m from a small
sphere with an excess of 1012 electrons. (-3.6 X 103 V; 9.0 x 103 N/C [towards sphere])
8.
Two horizontal plates of opposite charge form a constant electric field  = 1000 N/C directed
vertically downwards. An electron of mass me and charge e is fired horizontally with velocity
v = 0.1c, where c = 3.00 x 108 m/s between the plates. Calculate the electron’s acceleration.
**Optional: (If the plates have length 1 m, find the electron’s deflection from the horizontal
when it emerges.)** (1.76 x 1014 m/s2; 0.098 m upward)
9.
A horizontal east-west wire carries a westward current. A beam of positively charged
particles is shot directly down at the wire from above. In what direction will the particles be
deflected?
10.
An α-particle (He-nucleus) of charge +3.2 x 10-19 C and mass 6.7 x 10-27 kg first accelerates
through a potential difference of 1.2 x 103 V, then enters a uniform magnetic field of
magnitude 0.25 T at 90°. Calculate the magnetic force. (2.7 x 10-14 N)
\sph4U\electrostatics\769827671
1(d); 2(d); 3(b); 4(e); 5(c)
11.
A straight wire 15 cm long, with a current of 12 A, lying at right angles to a uniform magnetic
field, experiences a magnetic force of magnitude 0.40 N. What is the magnitude of the
magnetic field? (0.22 T)
12.
A conductor 45 cm long, with a mass of 15 g, lies in a horizontal position at 90 angle to a
uniform horizontal magnetic field of magnitude 0.20 T. What must the current in the
conductor be if the magnetic force is to support the weight of the conductor? (1.6 A)
13.
Describe as many of the similarities and differences between electrostatic fields,
gravitational fields and magnetic fields.
Some multiple choice questions.
1.
Two small spheres, having positive charges of X units and Y units respectively, are located 10
m apart. A test charge of +1 unit is located between them 2 m from X and 8 m from Y. The
net electrical force on the test charge is zero. The ratio X:Y is
a)
16:1
b) 4:1
c)
1:4
d)
1:16
e)
1:1
2.
Which of the following statements if false for a charged particle between two parallel plates
having a voltage, V between them?
a)
the electric force on a positive charge is in the same direction as the electric field
b)
the magnitude of the electric force is the same anywhere between the plates
c)
the electric force on a negative charge is in the opposite direction to that of the
electric field
d)
the magnitude of the force on a positive charge is greater than the magnitude of the
force on a negative charge
e)
the electric force on the object is proportional to the voltage on the plates
3.
The
a)
b)
c)
d)
e)
4.
When two small charged spheres are separated by 2.0 m, the electrical force of attraction
between them is 6.0 N. If the charge on each sphere is doubled and the separation is
reduced to 1.0 m, the force of attraction will now be
a)
6N
b)
16 N
c)
24 N
d)
48 N
e)
96 N
5.
Two spheres, X and Y, are 4 m apart. A charge of 2Q is distributed over sphere X and a
charge of Q is distributed over sphere Y. The magnitude of the electrostatic force on X is
a)
4 times that on Y
d)
0.5 times that on Y
b)
2 times that on Y
e)
0.25 times that on Y
c)
the same as that on Y
electric field at a point near a charge Q represents
the energy possessed by a unit positive charge
the force acting on a unit positive charge
the energy possessed by a unit negative charge
the force acting on a unit negative charge
the amount of work which could be done by a unit positive charge
Text M/C:
\sph4U\electrostatics\769827671
p. 304 #19, 24, 25, 26, 28
p. 432 #15-21, 23-25
1(d); 2(d); 3(b); 4(e); 5(c)