# Common Long question answers - physics

PhysicsB

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• Created on: 17-04-12 11:08

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Physics
EXPLAIN WHAT AN EDDY CURRENT IS, HOW IT IS PRODUCED IN THE RING AND HOW DIRECTION
OF CURRENT IN THE RING COMPARES WITH THAT IN COIL?
Eddy currents are circulate currents that oscillate within the ring
Changing coil in the coil produces changing magnetic field
Emf is induced in the ring
Direction of current in the ring sets up a field to oppose the change in the field produced by
the coil
If coil currents increases ring current is in opposite direction to oppose the increase in field.
FACTORS THAT AFFECT THE MAGNIUDE OF THE INDUCED CURRENT IN THE RING!
Rate at which flux is cut ­ faster it is cut the higher the induced emf
Circumference of the ring ­ longer path for the current so higher resistance and lower
current
Resistance of the ring ­ lower resistance higher current (relate to equation V=IR)
Thickness of the ring ­ the thicker the ring lower the resistance so higher the current
Depth of the ring ­ magnetic field weaker so emf is smaller.
EXPLAIN WHY THE GRAVITATIONAL POTENTIAL ENERGY HAS A NEGATIVE VALUE!
Gravitational potential is zero at infinity
Work is done on the object in bringing it from infinity to earth's surface/ potential increase as
object is lifted higher
Energy is lost from zero which means it must be zero
HOW IS PROPULSION ACHIEVED WITH A LIQUID PROPELLANT ROCKET?
Fuels react in combustion chamber
High temperature and pressure gasses are ejected through the nozzle
Initial momentum is zero
The total momentum is also zero as no external forces act on it
Momentum of gases mean that there must be momentum in equal and opposite direction
HOE DOES FARADAYS' LAW AND LENZ'S LAW RELATE TO THE INDUCTION OF EDDY CURRENTS IN
METAL OBJECT?
Changing flux produced by the transmitter cuts the metal object
This induced emf and therefore eddy currents in object
Eddy currents produce field of direction opposing change
WHY DO X-RAYS SPECTRUM HAVE SHARP PEAKS?
Electrons (striking target) eject inner electrons of target material
Outer electrons fall to fill vacancies
Change of energy levels results in photon being emitted
WHAT IS MEANT BY ESCAPE SPEED?
Speed with which an object escapes gravitational field

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EXPLAIN HOW A RIDER EXPERIENCES THRILL (RELATE TO DESIGN OF THE RIDES AND THE
DANGERS TO THE RIDER)!
Rapid change in direction/speed
Changes in height above the ground
Weightlessness
Large acceleration so bug `g' force
Larger acceleration so larger force
Acceleration equals thrill
Force can harm the rider
Repetitive vibrations act like driving oscillation
Resonance of body can lead to injury
Strapped in to reduce the effect of inertia when direction changes…read more