# Solve: Magnetic Field on a Compass

Question: A power line is 3.5m off the ground and is carrying 75 amps. A man standing under the power line is holding a compass 1.25m off the ground.

1) How large is the magnetic field produced on the compass by the power line?

2) If the power line runs east and west, how does its magnetic field affect the direction in which the compass points?

3) If the power line runs north-south, how does the magnitic field affect the direction in which the compass points?

https://brainmass.com/physics/power/solve-magnetic-field-on-a-compass-9961

#### Solution Preview

1.)

Because,

Distance/height of the power line from the ground = 3.5 m

Distance/height of the observer from the ground = 1.25 m

Hence,

Distance of the observer from the power line (r)= 3.5-1.25 = 2.25 m

current in the power line (I)= 75 A

Because, magnetic field due to current carrying conductor:

B = k*2*I/r

Here, k= mu_o/4pi = 10^(-7) N/A^2

=> B = 10^(-7)*2*75/2.25 = 6.67*10^(-6) T = 6.67*10^(-2) Gauss

(because 1 Gauss = 10^(-4) T)

=> B = 0.067 Gauss (Answer) ...

#### Solution Summary

In about 340 words, including explanations and the appropriate calculations, the details for these three problems focused on the concept of magnetism are solved. A jpg document is also attached which corresponds to question two.

9 Physics word problems: Magnitude of compass needle, magnet, magnetic field, alpha particle speed, current, coil, galvanometer, resistance

1. A compass needle in a uniform magnetic field of 0.30 T experiences a torque of 0.050 N * m when it points in a direction 45 degrees away from the direction of the field. What is the magnitude of the needle's magnetic moment?

2. A slender, 150-g bar magnet 15.0 cm long has a magnetic moment of 5.30 x 10^6 A * m^2. It is held at an angle of 45 degrees to the direction of a uniform magnetic field. When released, it begins to rotate about its center with an intial angular acceleration of 5.09 x 10^-3 rad/s^2. What is the magnitude of the magnetic field.

3. A wire 0.250 m long carries a current of 0.750 A in a region of uniform magnetic field. The wire is subject to a force of 2.50N when held perpendicular to the direction of the field. What is the magnitude of the magnetic field?

4. Alpha particles from a particular radioactive source have a speed of 1.85 x 10^7 m/s. How large a magnetic field is required to bend the path of the particles into a circle of 0.580-m radius? An alpha particle has a mass of 6.64 x 10^-27 kg and a charge of 3.20 x 10^-19 C.

5. A long straight wire carries a current of 100mA. What is the magnitude of the magnetic field 10.0cm from the wire?

6. Two parallel wires spaced a distance d apart experience an attractive fore per unit length of 6.00 x 10^-4 N/m. If the currents have a magnitude of 10.0A each, what is the distance d?

7. A coil of 32 turns of wire is wound about a circular form. The average diameter of the individual loops is 28.5 cm. Calculate the magnetic moment of the coil when it carries a current of 1.75A.

8. A lab technician needs to make an ammeter that measures 15 A full scale. The only galvanometer available deflects full scale as a current of 100 microA, and its resistance is 10kOhm. What resistance is needed and how should it be connected to the galvanometer?

9. A student needs to make a voltmeter that measures 200V full scale. The only galvanometer available deflects full scale at a current of 10.0 mA, and its resistance is 1.00 kOhm. (a) What resistance is needed and how should it be connected to the galvanometer? (b) Draw a circuit diagram for the resulting meter.

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