1. One long straight wire carries a current of 7.5A. A 2.00m length of a second

Question

1. One long straight wire carries a current of 7.5A. A 2.00m length of a second wire carries a current of 9.75A parallel to the first wire. The two wires are 5cm apart. Determine the force on the second wire due to the first.

2. When an automobile moves at 15 m/s, its axles experience an emf of .00110 V. If the component of the earth's magnetic field perpendicular to the car's velocity and to its axles is 3.00x10^-5 T, find the length of each axle.

3. A 450-turn coil of diameter 2cm experiences an axial magnetic field of 1.6T. The field is reduced to zero, yielding an induced emf of 6V. How much time did it take for the field to drop to zero?

Explanation / Answer

1)the force is

F = (u_o x I1 x I2/2pi x d)

where u_o = 4pi x 10^-7 Tm/A,I1 and I2 are currents and d is separation between the wires

2)the speed is v = 15 m/s

the emf is V = 0.00110 V

the magnetic field is B = 3.00 x 10^-5 T

let E be the electric field

we know that

v = (E/B)

or E = v x B

Also,

V = E x L

or L = (V/E)

where L is length of axle

3)the number of turns is N = 450

diameter is d = 2 cm

radius is r = (d/2) = 1 cm = 1 x 10^-2 m

the magnetic field is B = 1.6 T

induced emf is V = 6 V

let I be the current

we know that

B = (u_o x N x I/2pi x r)

or I = (B x 2pi x r/u_o x N)

where u_o = 4pi x 10^-7 Tm/A

Also,

V = I x R

or R = (V/I)

the time required is

t = R x C

where C is capacitance

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