# Electromagnetic effects and Magnetic Fields Questions

• lpettigrew
In summary, when two parallel wires carry current in the same direction, they exert equal and opposite attractive forces on each other. The induced emf is measured in volts, equal to one joule per coulomb. The incorrect unit for emf would be anything that is not equivalent to a volt. The Earth's magnetic field has a vertical component that can induce emf across the wings of a flying object, regardless of the direction it is traveling. A magnetic force is exerted on charged particles when they move perpendicular to the field lines in a magnetic field. However, this can also apply to macroscopic objects such as paper clips.

#### lpettigrew

Homework Statement
I have been learning about electromagnetic effects recently and while revising have found several, relatively straight forward problems. However, my understanding of this topic is rather inexperienced and therefore I wondered whether anyone could dispense any further comments about how to improve my responses.

1. What force will two long parallel wires carrying a current in the same direction exert?
2. A 20 mm long conductor is positioned within a magnetic field of flux density of 0.10 T. The conductor is moving in a direction at 30 degrees to the field at at speed of 5ms^-2. Find the value of the induced EMF.
3. In what direction would an aircraft flying horizontally have to fly to induce an emf across its wings?
4. What would be an incorrect unit for emf?
5. A conductor of length 20 mm is carrying a current of 5 A and is situated in a magnetic field of flux density 0.10 T. If the current is flowing in a direction at 30 degrees to the field lines find the magnitude of the force on the wire?
6. What experiences a force in a magnetic field?
7. What is the value of flux when the magnetic flux through a coil of 5 turns is uniformly increased from zero to a final value in 10 s, inducing an EMF of 0.03 V across the coil?
Relevant Equations
F = BILsinθ
ε= ΔNΦ/Δt
1. When two parallel wires carry current in the same direction, they exert equal and opposite attractive forces on each other.

2. ε=lvBsinθ
ε=0.02*5*0.1*sin30
ε=0.005 V

3. Well, a conductor moving through a magnetic field has the potential to induce an emf, but this movement must be in such a direction that the conductor cuts through the lines of magnetic flux, and will be a maximum when it moves perpendicular to the field. Would this imply that this occurs when the plane travels from East to West?

4. In S.I. units, emf is measured in volts, equal to one joule per coulomb. Therefore would the incorrect unit be AΩ^-1 or perhaps Wbs^-1?

5. F = BILsinθ
F=0.1*5*0.02*sin30
F=0.005 N

6. A magnetic force will be exerted when a charged particle moves perpendicular to the field, therefore, a charged particle whose velocity has a component perpendicular to the field lines will experience a force when positioned in a magnetic field.

7. Rearranging the formula for induced emf;
ε= ΔNΦ/Δt
Φ=εt/N
Therefore Φ=0.03*10/5=0.06 Wb

I would be very grateful for any assistance and truly just want to better understand this subject area

Delta2
I would just like to work with one item at a time. For (3), the Earth's magnetic field in many places has a vertical component to it. I think it will be the vertical component that makes for the EMF across the wings, and I don't think the direction matters, so long as there is a vertical component to the Earth's magnetic field.

In flying east and west, the EMF will be from bottom to top and visa versa.

Last edited:
Delta2
lpettigrew said:
4. In S.I. units, emf is measured in volts, equal to one joule per coulomb. Therefore would the incorrect unit be AΩ^-1 or perhaps Wbs^-1?
Anything that's not equivalent to a volt would be an incorrect unit. But Wb/s is equivalent to a volt, isn't it?

6. A magnetic force will be exerted when a charged particle moves perpendicular to the field, therefore, a charged particle whose velocity has a component perpendicular to the field lines will experience a force when positioned in a magnetic field.
This question does seem a little vague. Your answer is correct as far as charges go. But I can think of macroscopic objects, like paper clips, that experience a force in a magnetic field, so you could expand on your answer.

Delta2