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20 Cards in this Set
- Front
- Back
What is the difference between a step up and step down transformer? |
step up: Ns>Np Vs>Vp step down: Nsp Vsp |
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How does kinetic energy change around a non-circular orbit? |
When closer, PE is smaller and KE is bigger due to bigger attractions and small radius When further away PE is greater, the force of attraction is less, so velocity and therefore KE is smaller |
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What is a couple? |
A coil of wire in a magnetic field, the coil rotates and each side feels an equal but opposite force |
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How do you work out torque on a couple in a magnetic field? |
Torque is the turning force Torque = Fwcos_alpha_ Fwcos_alpha_= BILnwcos_alpha_BILnA |
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How do you work out force on a moving charge in a magnetic field? |
F=BQvsin_theta_ when velocity at angle _theta_ to magnetic field |
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How do you work out the radius of the orbit of a moving charge in a magnetic field? |
r= mv/BQ (remember specific charge is Q/m) |
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How do you work out the time period of the orbit of a moving charge in a magnetic field? |
t=2_pi_m/BQ (remember specific charge is Q/m) |
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How does a cyclotron work? |
A cyclotron is 2 semicircle electrodes with a gap. Particles are accelerated across the gap, which makes speed and radius increase. An alternating current is used to make the particles cross the gap. The time period stays the same. Uses include medical imaging and cancer therapy. |
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What is magnetic flux? |
symbol _phi_ the number of magnetic field lines in an area phi=BA units: weber (wb) 1wb=1Tm^2 Area and magnetic flux are perpendicular |
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What is magnetic flux linkage? |
A measure g the magnetic flux of a coil of wire N_phi_=BANcos_theta_ |
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What is electromagnetic induction? |
If there is relative motion between a wire and magnetic field, an emf is induced in the wire |
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How does electromagnetic induction work? |
The electrons in the wire experience a force which causes them to move to one end of the wire. A current is induced if the wire is part of the circuit. No emf is induced if the wire is parallel to the magnetic field |
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How do you increase the end induced in electromagnetic induction? |
Move the wire or magnetic field faster Use a stronger magnet Use a coil of wire and increase the number of turns |
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What is Lenz’s law? |
The direction of the induced current opposes the change that caused it |
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What is Farraday’s law? |
The induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit epsilon=-N_deltatheta_/_delta_t |
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What is the difference between AC and DC? |
AC uses a slip ring commutator- current leaving changes every 180 degrees DC uses a split ring commutator- the current leaving is always in the same direction |
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What is the peak voltage on an oscillator? |
Distance between the peak and equilibrium |
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What is the peak voltage on an oscillator? |
Distance between the peak and equilibrium |
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What is Irms? |
The current in DC that would give the same hearing effect as AC (same for Vrms) |
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What are transformers? |
Used in the National Grid, they are used to change pd (peak value of alternating current). Flux is the same as the iron core is the same all the way round. |