last time: how charged particles move in a magnetic field. consider a uniform magnetic field into...
TRANSCRIPT
![Page 1: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/1.jpg)
Last time: how charged particles move in a magnetic field.
Consider a uniform magnetic field into the board, with conducting rod moving through it:
𝑣
+ side
- side
Charges will move
If part of a circuit, can generate a current!
![Page 2: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/2.jpg)
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.
![Page 3: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/3.jpg)
Magnetic Flux
Just like for electric fields, can define magnetic flux through surface:
For uniform and a flat surface :
![Page 4: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/4.jpg)
Faraday’s LawChanging magnetic field can induce a and
where is the magnetic flux.
- Solenoid with alternating / direct current.
- Vary number of windings.
![Page 5: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/5.jpg)
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?
![Page 6: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/6.jpg)
B B
Top View
Wire Loops
Solenoids
Magnetic field ~inside of solenoid only area is the same for both flux is the same for both.
![Page 7: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/7.jpg)
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
![Page 8: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/8.jpg)
Lenz’s Law
The induced current creates a magnetic field that opposes the change in magnetic flux through the area enclosed by the loop.
Way to interpret the minus sign in Faraday’s Law
![Page 9: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/9.jpg)
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. Clockwise2. Counter-clockwise3. No current is induced
![Page 10: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/10.jpg)
The loop shown below is traveling towards the wire with the velocity shown. The current, , is constant. In which direction is the induced current in the loop?
1. Clockwise2. Counter-clockwise3. No current is induced
![Page 11: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/11.jpg)
The loop shown below is traveling towards the right at a constant distance from the bottom wire. The current, , is constant. In which direction is the induced current in the loop?
1. Clockwise2. Counter-clockwise3. No current is induced
𝑣
![Page 12: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/12.jpg)
Cool Application: Generators and Motors
![Page 13: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/13.jpg)
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 above7) All except 2)8) All except 3)9) All except 4)
![Page 14: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/14.jpg)
Relation to Electric Fields
Electric fields cause charges to move induced EMF can be related to :
where integral is a closed path.
Note: Not necessary for a loop to be there (i.e., test charges) for an field to be created.
![Page 15: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/15.jpg)
Eddy Currents
Plate moving between poles of magnet:
Force tends to damp motion of the plate.
N
S
F
S
NF
![Page 16: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/16.jpg)
Adding slots fewer paths for current higher resistance less force.
![Page 17: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/17.jpg)
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).
![Page 18: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/18.jpg)
Lab:
Magnetic Field of a Slinky:- Magnetic field sensor w/ LoggerPro- Do theoretical predictions about
magnetic field hold?
In terfaceV mV
Pow er supply
Sw itch
Am m eter
![Page 19: 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](https://reader035.vdocuments.mx/reader035/viewer/2022062421/56649cd65503460f9499d4dc/html5/thumbnails/19.jpg)
Quantitative Question (31.12):
A coil of 15 turns and radius 10.0 cm surrounds a long solenoid of radius 2.00 cm and 1000 turns/meter. The current in the solenoid changes as, where is in amperes and t is in seconds. Find the induced emf in the 15-turn coil as a function of time.