How Do Moving Conductors and Coils Interact with Magnetic Fields?

[astronomyabc]

Homework Statement

1) The coil of a moving-coil loudspeaker has a mean diameter of 30mm and is wound with 800 turns.It is situated in a radial magnetic field of 0.5T. Calculate the force on the coil, in Newtons, when the current is 12mA.

2)Explain what happens when a long straight conductor is moved through a uniform magnetic dirld at constant velocity.Assume that the conductor moves perpendicularly to the field.If the ends of the conductor are connected together through an ammeter, what will happen?

3)A copper disc,250mm in diameter, is rotated at and prependicular to its plane. If the axis points magnetic north and south, calculate the e.m.f between the circumference of the disc and the axis. Assume the horizontal component of the Earth's field to be 18uT.

Homework Equations

The Attempt at a Solution

i don't know how to calculate the above questions.but i try to solve Q2 as the follow,please give me some advice and solution,thanks

Q2 ans. A deflection was obtained on ammeter,when the direction of moving of conductor was reversed,ammeter was also deflected in the reversed direction.

 

[Mindscrape]

The first question you have a solenoid, have you learned what to do with these?

The second you are right.

The third question requires Faraday's Law.

Try it out.

 

[m2003]

As an electromagnetic physicist, I can provide you with the necessary equations and steps to solve these problems. For the first question, we can use the equation F = BIL, where F is the force, B is the magnetic field strength, I is the current, and L is the length of the coil. Since the coil is circular, we can use the formula for the circumference of a circle to find the length, which is 2πr, where r is the radius. In this case, the radius is half of the mean diameter, so it is 15mm or 0.015m. Thus, the length of the coil is 2π(0.015) = 0.094m. Now, we can plug in the given values to find the force:

F = (0.5)(0.094)(800)(0.012) = 0.45 N

For the second question, when a conductor is moved through a uniform magnetic field at a constant velocity, an electric current is induced in the conductor due to the changing magnetic field. This is known as electromagnetic induction. The direction of the induced current is determined by Lenz's law, which states that the induced current will flow in a direction that opposes the change in magnetic field. In this case, the conductor is moving perpendicular to the field, so the induced current will be in a direction perpendicular to both the velocity and the field. This can be demonstrated using the right-hand rule.

If the ends of the conductor are connected together through an ammeter, the current will flow through the circuit and the ammeter will register a deflection. As you correctly stated, when the direction of the conductor's motion is reversed, the ammeter will also deflect in the opposite direction, as the induced current will also flow in the opposite direction.

For the third question, we can use the equation E = BLv, where E is the electromotive force (emf), B is the magnetic field strength, L is the length of the conductor (in this case, the circumference of the disc), and v is the velocity of the conductor. We also know that the emf is equal to the rate of change of magnetic flux, which is given by BA, where A is the area of the conductor. Since the disc is rotating perpendicular to its plane, the area A is equal to the area of a circle, πr^2, where r is the radius of the