Chapter 9 Energy, Power and Resistance Flashcards
What is the definition of potential difference?
Potential difference is a measure of the transfer of energy by charge carriers.
Define the volt?
A volt is the p.d across a component when 1J of energy is transferred per unit charge. The term potential difference is used when the charge carriers lose energy in a component.
What is the electromotive force of a cell?
It is the P.D of a cell where the charge carriers are gaining energy.
What is thermionic emission?
The emission of electrons through the action of heat.
What is the definition of resistance?
Resistance is the ratio between p.d and current
What is Ohms law?
For a metallic conductor kept at constant temperature the current in the wire is directly proportional to the p.d across its ends
How does increasing the temperature of a wire decrease its resistance?
As the temperature increases the current decreases and so the resistance increases this is because the ions in the wire are vibrating more and making it more difficult for the charge carriers to flow.
What does the current-voltage graph look like for a resistor and what feature of the graph tells you about its resistance?
It is a straight line through the origin and the gradient shows the resistance. steep gradient shows low resistance and shallow gradient shows high resistance.
What does the current-voltage graph look like for a filament lamp?
It is an S shape which passes through the origin. This S shape is because as the current increases so does the temperature and ?????
What are the features of a graph which is an ohmic component?
The line passes through the origin and is directly proportional
What is the special feature of a diode?
A diode only allows current to flow in one direction
What does the current-voltage graph look like for a diode?
The shape of the graph is at 0 before the p.d goes positive and then shoots up. Therefore the diode has very little resistance.
What is the resistivity of a material?
The resistivity is a property of a material.
The resistivity of a material at a given temperature is the product of the resistance and the cross-sectional area divided by its length.
What can change the resistivity of a material?
An increase or decrease in temperature.
What does a low resistivity mean?
It is a good conductor.
