MAGNETISM MAGNETISM BASICS MAGNETIC FORCES MOTORS AND GENERATORS

TOPIC 3 – MOTORS AND GENERATORS Learning Goal: You will be able to describe how the interaction between magnetism and electricity explains how motors and generators work. Success Criteria: You will know you have met the learning goal when you can truthfully say: 1.I can describe how motors and generators work. 2.I can calculate the current produced by a generator. 3.I can calculate the force on the loop in a motor. Image(s) from Bing Images

I can describe how motors and generators work An electric generator, often just called a generator, is a device that when work is done on it, creates an electric current. A motor is a device that does the opposite, turning an electric current into work. Put another way, you do work on a generator to produce electricity, and you use electricity to make a motor do work. Image(s) from Bing Images InputOutput GeneratorWorkElectric current MotorElectric currentWork

I can describe how motors and generators work Image(s) from Bing Images

I can describe how motors and generators work Task 8.3.1(4 points): Answer these questions. a)What does a generator do? b)Why is it necessary to move the loop of wire through the magnetic field to produce an electric current? c)What does a motor do? d)Why is it necessary to switch the direction of current energy half turn in order to keep the loop turning? Image(s) from Bing Images

I can calculate the current produced by a generator. The maximum voltage produced by a generator can be changed according to this equation: V max = NAB2 π f V max is the voltage produced when the loop is parallel to the magnetic field lines (V). N is the number of turns of wire in the loop (integer). A is the area of the loop (m 2 ). B is the magnetic field the loop is moving through (T). f is the frequency, or the number of complete turns the loop makes per second (Hz, or s -1 ) Image(s) from Bing Images

I can calculate the current produced by a generator. Since the voltage depends on the orientation of the wire and the magnetic field, the effective voltage is lower than the maximum: ACDC The root mean square of the maximum voltage is more accurate for determining the effective voltage provided by a generator: V rms = V max x Image(s) from Bing Images

I can calculate the current produced by a generator. You can then use V = IR to find the maximum and effective current and P = IV = I 2 R = V 2 R to find the maximum and effective power (note that “rms” and “effective” are used interchangeably). For current: V max = I max R V rms = I rms R For power: P max = I max V max = I max 2 R = V max 2 R P rms = I rms V rms = I rms 2 R = V rms 2 R If you work it out, you’ll see that: P max = 2P rms

I can calculate the current produced by a generator. Task (7 points): Find the wanted information: a)You create a generator by wrapping a wire 480 times around a rectangular loop with area m 2. If you place the loop in a 0.25 Tesla magnetic field, what will be the maximum voltage if you turn it 20 times per second? b)What would the effective voltage be for the generator in part a)? c)If the wires in part a) were to provide 314 ohms or resistance, what would the maximum and effective current be in the wire? d)What would the maximum and effective power be for the generator in part a)?

I can calculate the current produced by a generator. Task (7 points): Find the wanted information: e)You measure the effective power of a generator to be 8.2 watts. If the effective current produced by the generator is measured to be 0.30 A, what is the effective and maximum voltage produced by the generator? f)If the generator in part e) had a m 2 loop with 1300 turns of wire around it and were being turned 32 times per second, what would the strength of the magnetic field be around the generator? g)You have magnets that produce a 0.13 T magnetic field between them. How many turns of the wire would you need if you could turn it 4 times per second and the area of the loop were 142 cm 2 (there are 10,000 cm 2 in 1 m 2 )

I can calculate the force on a loop in a motor. When voltage is applied to the wire loop in a generator, the force on the wire from the magnetic field can be measured as a function of a few of the factors we have discussed so far: F = 2NBIL F is the force on the wire by the magnetic field (N). N is the number of turns of the wire (no units). B is the strength of the magnetic field (T). I is the current through the wire (A). L is the length of the side of the loop that runs perpendicular to the magnetic field (m).

I can calculate the force on a loop in a motor. You can see from the right hand rule that when the loop is perpendicular to the magnetic field, it will no longer move. At this point, the current has to switch directions, which is done by changing which end of the wire is connected to the positive terminal and which is connected to the negative terminal. This is done with a commutator, a ring with a gap in places allowing for the direction of current to be altered. A rod is then attached to the loop which can be used to turn a gear, thus performing the work the motor was designed for. Image(s) from Bing Images

I can calculate the force on a loop in a motor. Task (5 points): Find the wanted information: a)When a 1.0 A current is run through a loop of wire with 220 turns in it that has been placed in a 0.75 T magnetic field, what would the force on it be if the length of the loop were 18 cm? b)Suppose you make a motor with 506 turns of wire where the length of the loop is 2.4 cm. If it is placed in a 0.12 T magnetic field, what current would you have to run through it for the force on the wire to be 1.6 N? c)How many turns of a wire would you have to give the wire loop in a motor for it to feel a 10.0 N force on it if the loop were 82 mm long and connected to a 9.0 V battery and placed in a 0.74 T magnetic field. The resistance of the wire is measured as 78 ohms.

I can calculate the force on a loop in a motor. Task (5 points): Find the wanted information. d)What would making the following changes do to the force acting on the wire? Doubling the number of loops. Doubling the length of the loop. Doubling the strength of the magnets. Doubling the current. Doubling the voltage that powers it. (think hard about this one) e)Make a T-chart and say what factors would contribute to a stronger motor, such as “low current” vs “high current”.

Task (4 points): Write at least 8 things you learned in this topic (1/2 point each). If you do this in your notebook, please do it in list form, rather than paragraph form. Image(s) from Bing Images