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### AuthorTopic: TSFX 2005 Phys trial exam  (Read 853 times) Tweet Share

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#### Ninox

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##### TSFX 2005 Phys trial exam
« on: November 13, 2007, 05:23:18 pm »
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Hey everyone,
I just need some help with question 4. Electric Power.

An aeroplane with a wing span of 40m flies over the North Magnetic Pole at 120m/s. The Mag. field strength is 5x10^-4 T.
a) What is the induced EMF?

They use the formula F = BLv =2.4 Volts
I don't quite get how this works though.
Thanks

Good luck with the exam tomorrow
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#### Galelleo

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##### TSFX 2005 Phys trial exam
« Reply #1 on: November 13, 2007, 05:28:56 pm »
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Ok.

the wings are basically linear, so you can assume they will be treated as a rod moving through a magnetic field. the formula for that is BLv because...

emf = BA/t .... A= (ina  square lengthxwidth) which are measures of distance... so you have BxLxL/t ... L/t (length on time) is velocity... because if the length of the wingspan is considered length in one direction, its movement forward is considered the other... so we can use velocity.

therefore BL x L/t = BLv.

BLv = 5x10^-4 x 40 x 120 = 2.4
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#### Galelleo

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##### TSFX 2005 Phys trial exam
« Reply #2 on: November 13, 2007, 05:29:25 pm »
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But you shuold just know the formula E(voltage) = BLv... hurry, go write it on your cheat sheet ! !:P
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#### Galelleo

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##### TSFX 2005 Phys trial exam
« Reply #3 on: November 13, 2007, 05:30:24 pm »
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I dont like this question tho, because the rod is moving horizontally, as well as its got width and depth ( hence volume), so you would expect to have to use area

i doubt VCAA would use this sort of example because we tend to focus on 2 dimensions.
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#### Ninox

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##### TSFX 2005 Phys trial exam
« Reply #4 on: November 13, 2007, 05:44:03 pm »
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Quote from: "Galelleo"
Ok.

the wings are basically linear, so you can assume they will be treated as a rod moving through a magnetic field. the formula for that is BLv because...

emf = BA/t .... A= (ina  square lengthxwidth) which are measures of distance... so you have BxLxL/t ... L/t (length on time) is velocity... because if the length of the wingspan is considered length in one direction, its movement forward is considered the other... so we can use velocity.

therefore BL x L/t = BLv.

BLv = 5x10^-4 x 40 x 120 = 2.4