Chapter 9: Energy, Power and Resistance Flashcards
battery
two or more cells connected end to end, or in series
What are the rules when drawing a circuit?
1) only use the circuit symbols
2) do not leave any gaps between the wires
potential difference
measure of transfer of energy by charge carriers, work done by charge carriers
volt
pd across a component when 1J of energy is transferred per unit of charge passing through a component
equation for voltage with charge
V = W/Q
voltmeter
measures potential difference
ideal voltmeter
infinite resistance
electromotive force
when work is done on charge carriers, gain energy when passing through the battery or cell
electron gun
a device used to produce a narrow beam of electrons, used to ionise particles
How do electron guns work?
- small filament heated by current
- electrons gain enough energy to escape atoms
- If filament is in vacuum and high PD is applied between filament and anode, the filament becomes a cathode
- free electrons accelerate towards the anode
- anode has a small hole and electrons in line pass through the hole, creating a beam
thermionic emmission
electrons getting enough energy to escape their atoms
energy transfer equation
work done on electron = gain in kinetic energy
eV = 0.5 x m x v2
What does LINAC stand for?
linear particle accelerator
How does a LINAC work?
series of cylindrical tubes to accelerate subatomic particles such as electrons.
There is a polarity in the tubes that alternates between positive and negative with precise timing
Every time an electron moved from one tube to another it gains energy (eV) where V is max emf of the alternating source connected to the tubes
What does a large number of electrodes mean?
electrons can be accelerated to extremely high velocities
Applications of LINACs
injectors for even higher energy particle accelerators
Hospitals to produce the X-rays required for radiotherapy
resistance
ratio between potential difference and current
What is the unit for resistance
ohms
What is ohms law?
in constant conditions, current is directly proportional to potential difference
what happens when the temperature of the wire increases?
positive ions vibrate with a greater amplitude about their mean position, and charge carriers do more work, and therefore transfer more energy when they travel through a wire
What is an ohm?
resistance of a component when a pd of 1V is produced per ampere of current
IV Characteristic
shows the relationship between the current and potential difference
How can you tell if a component is obeying Ohm’s Law through its IV characteristic?
straight gradient through the origin
what is the resistance of an ideal voltmeter?
infinite resistance
resistivity
resistance per meter length of material
what is the relationship between resistance and length?
directly proportional
what is the relationship between resistance and cross sectional area?
inversely proportional
equation for Resistance
R = V/I
Techniques and procedures used to investigate the electrical characteristics for a range of ohmic and non-ohmic components:
How does resistance vary with light intensity?
as the light intensity increases, resistance decreases
equation for resistivity
R X A / L
How do you calculate the resistivity of a metal?
1) measure length of test wire connected to the circuit
2) close switch and measure current and potential difference
3) open switch and calculate resistance
4) repeat and calculate mean
5) reposition flying lead and REPEAT
power equations
P = I V
P = I2 R
P = V2 / R
what is the unit of energy in electricity bills?
kilowatt-hour (kWh)
at what PD does a diode turn on?
0.7V
how would you describe the I-V Characteristic of a diode
threshold relationship
what is the difference between EMF and PD?
EMF is concerned with energy being put into the circuit while PD is concerned with the energy used by the components
