# Magnetic Field Inducing Electric Field - Lighting a 60W Bulb

• vaxopy
In summary, the problem involves determining the length of the rails on which a moving rod slides so that a 60.0-W light bulb with a resistance of 240 W can remain lit for one-half second. Using Faraday's law and the equation P = V^2/R, the velocity can be calculated as 120V and with the assumption of constant velocity, the length of the rails can be found by multiplying the velocity by 1/2 a second.
vaxopy
Suppose the light bulb in Figure 22.4b is a 60.0-W bulb with a resistance of 240 W. The magnetic field has a magnitude of 0.40 T, and the length of the rod is 0.60 m. The only resistance in the circuit is that due to the bulb. Minimally, how long would the rails on which the moving rod slides have to be, in order that the bulb can remain lit for one-half second?

Anyone know how i can start going about solving this :)?

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hrm...

Faraday's law states that the induced emf is equal to the negative rate of change of magnetic flux. Also the rate of change of magnetic flux is equal to B*dA/dt, since the magnetic field is completely perpendicular to the entire area.

Emf = B*dA/dt, you can relate this to the information given in the problem

remember that emf = I*R

i don't know much calculus

P = V^2/R
im assuming V = emf in the equation emf = vBL
so

60W = emf^2/240ohms
emf = 120V..

but they do not give me a velocity or anything
im stumped :/

The using that V = vBL you can solve for velocity. You already calculated V and B and L are given.

Assuming the velocity is constant you can just multiply 1/2 a second to find the rail length.

## 1. How does a magnetic field induce an electric field?

According to Faraday's law of induction, a changing magnetic field will induce an electric field. When an electrically conductive material, such as a wire, is placed in a changing magnetic field, the electrons within the material will experience a force and move, creating an electric current.

## 2. What materials are needed to light a 60W bulb using an induced electric field?

You will need a strong magnet, a wire, and a 60W bulb. The wire must be made of a conductive material, such as copper, and should be long enough to reach from the magnet to the bulb.

## 3. How does the strength of the magnetic field affect the brightness of the bulb?

The strength of the induced electric field is directly proportional to the strength of the magnetic field. Therefore, the stronger the magnet, the brighter the bulb will be.

## 4. Can any type of bulb be used with this method?

Yes, any type of bulb that can be powered by an electric current can be used with this method. However, the brightness may vary depending on the wattage of the bulb and the strength of the magnetic field.

## 5. Is this method safe to use?

Yes, this method is safe as long as the wire is properly insulated and there is no direct contact between the wire and the magnet. However, it is important to exercise caution when working with strong magnets to avoid any potential accidents.

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