Why use Doubtnut? Instant Video Solutions. Request OTP. Updated On: Share This Video Whatsapp. Text Solution. Answer :. Solution :. Very Important Questions.
The emf calculated in Example 1 above is the average over one-fourth of a revolution. What is the emf at any given instant? It varies with the angle between the magnetic field and a perpendicular to the coil. Figure 2. A generator with a single rectangular coil rotated at constant angular velocity in a uniform magnetic field produces an emf that varies sinusoidally in time.
Note the generator is similar to a motor, except the shaft is rotated to produce a current rather than the other way around. Charges in the wires of the loop experience the magnetic force, because they are moving in a magnetic field. Charges in the vertical wires experience forces parallel to the wire, causing currents. But those in the top and bottom segments feel a force perpendicular to the wire, which does not cause a current.
We can thus find the induced emf by considering only the side wires. The total emf around the loop is then. This expression is valid, but it does not give emf as a function of time. This can also be expressed as. Figure 3 shows a graph of emf as a function of time, and it now seems reasonable that AC voltage is sinusoidal.
Figure 3. The emf of a generator is sent to a light bulb with the system of rings and brushes shown. The graph gives the emf of the generator as a function of time. Note that the script E stands for emf. The greater the number of coils, the larger their area, and the stronger the field, the greater the output voltage.
This is noticeable on bicycle generators—at least the cheaper varieties. One of the authors as a juvenile found it amusing to ride his bicycle fast enough to burn out his lights, until he had to ride home lightless one dark night. Figure 4 shows a scheme by which a generator can be made to produce pulsed DC. Find the average emf induced in his wedding ring, given its diameter is 2. Integrated Concepts Referring to the situation in the previous problem: a What current is induced in the ring if its resistance is0.
An emf is induced by rotating a turn, Find the magnetic field strength needed to induce an average emf of 10, V. Integrated Concepts Approximately how does the emf induced in the loop in Figure 5 b depend on the distance of the center of the loop from the wire? Integrated Concepts a A lightning bolt produces a rapidly varying magnetic field. If the bolt strikes the earth vertically and acts like a current in a long straight wire, it will induce a voltage in a loop aligned like that in Figure 5 b.
What voltage is induced in a 1. The heat transferred will be 2. This is not a significant amount of heat. Skip to main content. Search for:. Determine the direction of the magnetic field B. Determine whether the flux is increasing or decreasing. Now determine the direction of the induced magnetic field B. It opposes the change in flux by adding or subtracting from the original field. Use RHR-2 to determine the direction of the induced current I that is responsible for the induced magnetic field B.
The direction or polarity of the induced emf will now drive a current in this direction and can be represented as current emerging from the positive terminal of the emf and returning to its negative terminal.
For practice, apply these steps to the situations shown in Figure 1 and to others that are part of the following text material. Applications of Electromagnetic Induction. The induced emf produces a current that opposes the change in flux, because a change in flux means a change in energy.
Energy can enter or leave, but not instantaneously. As the change begins, the law says induction opposes and, thus, slows the change. In fact, if the induced emf were in the same direction as the change in flux, there would be a positive feedback that would give us free energy from no apparent source—conservation of energy would be violated. Example 1. Move a bar magnet near one or two coils to make a light bulb glow.
View the magnetic field lines. A meter shows the direction and magnitude of the current. View the magnetic field lines or use a meter to show the direction and magnitude of the current. You can also play with electromagnets, generators and transformers! Click to download the simulation. Run using Java. Figure 6.
0コメント