09 energy, power and resistance Flashcards
What is 1 volt equal to?
1 coulomb gaining 1 joule of energy
Do voltmeters have high or low resistance?
High
What is n e.m.f?
Something that puts energy into a circuit
W=QV
What is a p.d?
Something that takes energy out of a ciruit
What is a byproduct of high resistance?
More energy is converted (heat)
Explain resistance.
Moving electrons collide with atoms in the wire, this transferees k.e to the wire causing it to heat up. As the wire heats up resistance increases as more collision happen.
What is ohms law?
V=IR, p.d=current x resistance
What is an example of a function of an electron gun?
old televisions
Briefly explain how an electron gun works?
The electron in the fillemant get hot and gain kinetic energy, as a result they can escape. Escaped electrons are projected through a small gap creating a ‘beam’ of electrons
3 factors affecting resistance:
- A= cross sectional area, bigger area small resistance
- material
- l = length, longer wire more resistance
What is the equation for resistivity?
R=(rho)L/A, measured in ohms meters
What happens to the area when you double the radius?
the area is x4
What is special about the current in a diode?
it only allows it to travel in 1 direction
What is a light emitting diode? (LED)
it emits light when current passes through it, used in circuits to indicate the direction of current flow.
Do diodes obey ohms law?
no
What is a negative temperature coefficient?
as temperature increases resistance decreases
