Formal assessment section 3 Flashcards
theextension of an elastic object is ___________ to the force applied , provided that the ___________ is not exceeded
directly proportional
limit of proportionality
what must happen to change the shape of an object?
more than one force must be applied
what does elastically deformed mean?
when an object returns to its original shape after the forces are removed
what does inelastically deformed mean?
when an object does not return to its original shape
what happens when the limit of proportionality for the extension of an elastic object and applied force has been exceeded? (3)
- doubling the force will no longer exactly double the extension
- the relationship becomes non-linear
- a force-extension graph will stop being a straight line
what is the equation for , extension , force, and spring constant
force= spring constant x extension
what is spring constant?
it indicates how easy it is to stretch or compress a spring- the higher the spring constant, the stiffer the spring.
when is the work done on the spring and the elastic potential energy stored not equal
when the spring is inelastically deformed
How do Loudspeakers work?
1) when a current flows through the coil, both the coil and the speaker core experience a force due to the magnetic field. The speaker core moves
2) Because the current is alternating when the direction of the current through the coil reverses, so too does the direction of the force exerted on it and the speaker core
3) this causes the speaker core to vibrate back and forth, producing a sound wave
4) the air around the core also vibrates creating variations in pressure that cause a sound wave
How do scrapyards work?
Scrap vehicles are lifted in a scrap yard using powerful electromagnets attached to cranes
when the current is turned on, the electromagnet attracts magnetic material below it
when the current is turned off, there is no more magnetic force
How do circuit breakers work?
this is a switch in series with an electromagnet, held by a spring
when the current is too large, the switch is pulled open by the electromagnet and it stays open until it is reset manually
How do electric bells work?
1) When the switch is pushed, the electromagnet is magnetised
2) The electromagnet attracts the armature
3) The hammer strikes the gong and breaks the circuit
4) the armature springs back, completing the circuit again and remagnetising the electromagnet
5) the cycle repeats for as long the button remains pushed
How do relays work?
Relays are used to switch an electrical machine on or off
1) a small current through the coil of the electromagnet magnetises the iron core
2) this pulls the armature onto the electromagnet, whose other end pushes the contacts together, completing the circuit.
3) When the current is switched off, the contacts open again, switching the circuit off.
How do microphones work?
1) Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet
2) This causes the coil of wire to move in the magnetic field, which generates current
* the diaphragm oscillates due to the changes in air pressure related to the sound wave
3) The microphone diagram and coil vibrate at the same frequency as the incoming sound. The bigger the amplitude of the sound, the bigger the amplitude of the vibration
4) this induces a potential difference and current in the coil with the same frequency of the incoming and wave and an amplitude dependent on the amplitude of the incoming wave
What is a convex lens?
What happens in a convex lens?
lens that curves outwards
rays of light are brought to a focus at the principal focus.