Energy, Power and Resistance Flashcards
Everything you need to know to get A* in OCR Physics A Level, closely following the specification and the textbook
What is the potential difference?
The energy transferred from electrical energy to other forms per unit charge
Define 1 volt
The potential difference across a component when 1 J of energy is transferred per 1C passing through the component
What is the electromotive force?
The energy transferred from chemical to electrical energy per unit charge, where work is done on the charge carriers
What is the difference between the electromotive force and potential difference?
Electromotive force is measure of energy given per 1C, but p.d. is measure of amount of energy used per 1C
How does an electron gun work?
A small metal element is heated by an electric current, and electrons are released through thermionic emission. The electrons accelerate through a high p.d. towards the anode, gaining KE. The electrons then pass through a hole in the anode, forming a beam of electrons
What is resistance?
The opposition to the flow of electric current
Define 1 ohm
The resistance of a component that has a potential difference of 1V per ampere
What is Ohm’s law?
The potential difference across a conductor is directly proportional to the current in the component as long as its temperature is constant
How does the resistance change when temperature increase?
When temp increase, positive ions inside wire have more internal energy and vibrate with greater amplitude. The frequency of collisions between charge carriers and positive ions increases, so charge carriers do more work, increasing the resistance
What is a diode?
A semiconductor component that allows current only in one particular direction
How does the resistance vary with the light intensity in an LDR?
As the light intensity increases, the resistance decreases
What is resistivity?
A property of a material that measures the extent to which it opposed the flow of electric current through it
How does the resistivity vary with temperature?
They are inversely proportional, so as temperature increases, resistivity decreases
What is a negative temperature coefficient?
A relationship in which a variable decreases as temperature increases
How does resistance vary with temperature for an NTC thermistor?
The resistance decreases as temperature increases
What is a kilowatt-hour?
A unit of energy
How many joules is one kilowatt-hour
3.6MJ
