Presentation on theme: "Last time: how charged particles move in a magnetic field. Consider a uniform magnetic field into the board, with conducting rod moving through it: + side."— Presentation transcript:
Last time: how charged particles move in a magnetic field. Consider a uniform magnetic field into the board, with conducting rod moving through it: + side - side Charges will move If part of a circuit, can generate a current!
Which direction is the current through the resistor? 1)Up 2)Down Note: as rod moves, there is an increasing magnetic flux through the loop.
What are ways that we can increase the amount of current through the loop? More windings? Angle of loop relative to solenoid? Shape of loop?
BB Top View Wire Loops Solenoids Magnetic field ~inside of solenoid only area is the same for both flux is the same for both.
In figure (a), a solenoid produces a magnetic field whose strength increases into the plane of the page. An induced emf is established in a conducting loop surrounding the solenoid, and this emf lights bulbs A and B. In figure (b), points P and Q are shorted. After the short is inserted, 1. bulb A goes out; bulb B gets brighter. 2. bulb B goes out; bulb A gets brighter. 3. bulb A goes out; bulb B gets dimmer. 4. bulb B goes out; bulb A gets dimmer. 5. both bulbs go out. 6. none of the above
Way to interpret the minus sign in Faraday’s Law
The current through the wire is decreasing and the loop is fixed relative to the wire. In which direction is the induced current in the loop? 1.Clockwise 2.Counter-clockwise 3.No current is induced
Cool Application: Generators and Motors
A uniform magnetic field can produce an EMF in a conducting loop if: 1)The field changes in magnitude. 2)The loop changes position within the field. 3)The loop rotates within the field. 4)The loop is removed from the field. 5)The loop changes size. 6)All of the above 7)All except 2) 8)All except 3) 9)All except 4)
Eddy Currents Plate moving between poles of magnet: Force tends to damp motion of the plate. N S F S N F
Adding slots fewer paths for current higher resistance less force.
Question: Let's say you take an ordinary wire coathanger and straighten out the hook shaped part that normally hangs over the coat rack. Now, you can spin the (roughly) triangular part around by twisting the straightened part between your fingers. Estimate the EMF that you can generate by spinning the hanger in the Earth's magnetic field (about 5.3 x 10⁻⁵ T).
Lab: Magnetic Field of a Slinky: - Magnetic field sensor w/ LoggerPro - Do theoretical predictions about magnetic field hold?