Chapter 9 - Energy, Power and Resistance Flashcards
Define potential difference V=W/Q
Work done by the charge carriers, the energy transfer per unit charge from electrical energy to other forms
Define electromotive force
Work done to the charge carriers, the energy transfer per unit charge from other forms to electrical energy
Definition of resistance
ratio of the potential difference across the component to the current passing through it
define the ohm
1 volt per unit ampere
Ohm’s Law
for a metallic conductor kept at constant temperature, the current in the wire is directly proportional to the potential difference across it
Explain why some components do not obey ohm’s law
As current increases, metal ions are heated, gaining kinetic energy and vibrate more around their fixed points. This increases frequency of collisions and so more work is done on the charged particles, increasing resistance
what are fixed resistors
resistance doesn’t vary, even with environmental changes
outline the functioning of diodes
- made of semiconductors allowing current to flow in only one direction
- if the diode is the wrong way round, resistance is infinite and current doesn’t flow
- if the diode is the correct way round, it does not conduct until the threshold value of p.d. is reached
NCT thermistor
as temperature increases, resistance decreases
LDR
as incident light intensity increases, resistance decreases
Define resistivity
the ability of a material to oppose the flow of charge
is resistivity dependent on dimensions
no, resistivity is independent of dimensions
Equation for resistance using resistivity
R= pL/A
Affect of temperature of resistance of metals and semiconductors
For a metal, increasing temperature fixed metal ions will vibrate more frequently increasing resistance. For semi conductors, increasing temperature increases the number density of charge carriers and so resistance decreases.
Electrical power
rate at which energy is transferred (W or Js-1)
