Download Two Identical charges, each -8.00 X 〖10〗^(

Two Identical charges, each -8.00 X 〖10〗^(-5) C, are separated by a distance of 25.0 cm. Find
the electric force between them?
Force
F
q1q2
4 0 r 2
Here F=?, q1 = q2 = -8*10-5C, ε0 = 1/(36pi*109)F/m, r = 25cms = 0.25m
Putting these values in the above expression, we get
5  105  5  105
F
1
2
4 

0.25
36  109
5  105  5  105  9  109

0.252
 360 N
As charges are identical, force will be repulsive.
What’s the electric force exerted on a test charge of 3.86 X 〖10〗^(-5) C if it is placed in an
electric field of magnitude 1.75 X 〖10〗^4 N/C?
F = QE
Here, F=?, Q = 3.86*10-5C, E= 1.75*10-4N/C
Hence, force F = 3.86*10-5C*1.75*104N/C
= 0.6755N
Find the resistance of 134 m of No. 20 copper wire at 20° C (p = 1.72 X 〖10〗^(-6) Ω cm, A =
2.07 X 〖10〗^(-2 ) 〖cm〗^(2 )).
Resistance is given by
R
l
A
Here R = ?, ρ = 1.72*10-6ohm-cm, l = 134m = 134*100cmsA = 2.07*10-2 cm2
Hence,
1.72 106 134 100
R
 1.1134
2.07 102
What is the cost to operate a 100 W lamp continuously for one week when the power utility rate
is 20 cents/kWh?
Energy consumed in a week

100  24  7
kWh
1000
Number of hours in a week = 24*7 and we divide by 1000 to get kWh.
Hence, cost of this energy
 20 
100  24  7
 336cents
1000
A 1000 W microwave, a 40.0 W fluorescent light bulb, and a 550 W computer are plugged into a
120 V parallel circuit.
What is the current passing through each appliance?
Current = P/V
Hence, current through microwave = 1000/120 = 8.33 A
Current passing through fluorescent light bulb = 40/120= 0.33A
Current passing through computer = 550/120 = 4.583A
Find the resistance of each appliance.
Resistance R = V2/P
Hence, microwave resistance = 120*120/1000 = 14.4 ohms
Fluorescent resistance = 120*120/40 = 360 ohms
Computer resistance = 120*120/550 = 26.18 ohms
A magnetic field can deflect a beam of electrons, but it cannot work on the electrons to change
their speed. Why?
Force on an electron acts in a direction perpendicular to the velocity of electron. We know that
work is given by W = F*r, where F = force and r = distance traveled in the direction of force. As
force F is acting in a direction perpendicular to direction of electron movement, the movement of
electron in the direction of force will be zero. Hence, work done on electron by magnetic field
will be zero.
Find the magnetic field at 0.500 m from a long wire carrying a current of 7.5 A.
Magnetic field around a wire in air is given by
B
0 I
2 r
Here B =? , I = 7.5A, r = 0.5m, μ0 = 4pi*10-7H/m
4 107  7.5
Hence, B 
 3 106Wb / m2
2  0.5
H = I/ (2*pi*r) = 7.5/(2pi*0.5) = 2.387A/m
An auto mechanic wants to use a solenoid she found on a car starter. If the solenoid is 0.150m in
length and has 750 turns of wire, what amount of current is required to produce a magnetic field
of 1.50 X 〖10〗^(-3) T at its center?
For a solenoid, H = NI/L
Hence, B = μ0H = μ0NI/L
Putting given values, we get
4  107  750 I
1.5  10 
0.15
1.5  103  0.15
I 
 0.2387, say 0.24 A
4  107  750
3
Write a paragraph to describe how a generator functions to generate power. Use common
electromagnetic physics terms, such as induction, coil, and current.
Electric generator works on the principle of electromagnetic induction. When a moving
conductor cuts magnetic lines of force, an electromotive force (emf) is generated at the ends of
the conductor. If the ends of the conductor are joined by a conductor, a current starts flowing
through the circuit thus formed. In a practical generator, many turns of conductor, called coil, is
rotated in magnetic field. To increase the voltage many coils are connected in series. When
current to be delivered by the generator is to be increased, coils are connected in parallel. The
energy consumed in rotating coils is converted into electrical energy in the form of current
passing through the external circuit.
Write a paragraph to describe the differences and similarities between a motor and a generator.
SIMILARITIES
Both motor and generator work on the principle of electromagnetic induction. Both are
electromechanical energy conversion devices and during the process of electromechanical energy
conversion, losses take place in both the devices. Hence, efficiency of both is less than 100%.
Rotation is essential in both motors and generators for electromechanical conversion process to
take place.
DIFFERENCES
Generator converts mechanical energy into electrical energy where as motor converts electrical
energy into mechanical energy. Hence, generators deliver the current and a motor takes the
current. Motors (generally a moving charge in a magnetic field) obey the Fleming`s Left Hand
Rule, while the generator obeys Fleming’s Right Hand Rule