Physics Flashcards
What is the efficiency equation?
Efficiency=useful energy out/total energy in
What is the equation for pay back time?
Pay back time=cost of insulation/energy bill saving
eg; if double glazing costs £150 but you save £50 a year on your energy bill , the pay back time is 3 yrs. 150/50=3
What is specific heat capacity?
the amount of energy needed to raise the temperature of 1kg substance by 1 degree Celsius. if something has a large specific heat capacity it will take longer to heat up as it needs more energy
What is the equation for specific heat capacity?
Energy (J) = mass (kg) x specific heat capacity (J/Kg degrees Celsius) x temperature change
What is the word equation for power?
power (W) = energy (J) / time (s)
Whats the word equation for units of electricity used?
units of electricity used (kWh) = power (kW) x time (hours)
Whats the cost equation?
cost = electrical energy used (kilowatt hours) x cost per kilowatt hour
What are longitudinal waves?
waves which oscillate parallel to the direction of travel eg sound waves
What are transverse waves?
waves which oscillate perpendicular to the direction of travel
What is the equation for wave speed?
Wave speed (m/s) = frequency (Hz) x wavelength (m)
What’s wrong with the Bohr model of the atom?
Not enough empty space and nucleus is too large
Should be incredibly small and dense
What are isotopes?
Have the same number of protons but different number of neutrons
What does alpha decay do?
In an attempt to become more stable, a very large nucleus will emit a fast moving helium nucleus (2 protons and 2 neutrons) we call this an alpha particle
What is beta decay?
In an attempt to become more stable, a nucleus which contains too many neutrons will emit a fast moving electron, we call this a beta particle.
The electron isn’t allowed to exist so is kicked out of the nucleus
The nucleus loses and electron and gains a proton so it becomes an atom of a new element
What is Gamma decay?
In an attempt to become more stable, a nucleus with too much energy will emit some of this energy as an electromagnetic wave.
There is no change to the nucleus when a gamma ray is emitted because only energy is lost
Describe why alpha beta and gamma are called ionising radiation
Alpha Beta and gamma collide with an atom
Gives some of their energy to the atom which makes it lose an electron
The atom becomes a positive ion
After each collision the ionising radiation loses kinetic energy
Eventually it loses too much energy and is no longer ionising radiation
What is ionising power?
The probability that the ionising radiation will ionise the atoms of the material it’s passing through
In other words: how likely it is that the ionising radiation will collide with the atoms
What’s penetration power?
What material or thickness of the material will stop the ionising radiation
In Other words: how likely it is that the ionising radiation will not collide with atoms. How far through a material it can get and what can stop it
What has the largest ionising power?
Alpha radiation
What has the smallest ionising power?
Gamma radiation
What has the largest penetration power?
Gamma radiation
What has the smallest penetration power?
Alpha radiation
What does half life mean?
The half life of a substance is the amount of time that it takes for half the unstable nuclei to decay
Can we predict when an individual nuclei will decay?
No as radioactive decay is a random process
What’s nuclear fission?
Is splitting the nucleus of an atom
The process is used to produce energy in nuclear power plants
Who does the nuclear fission process begin?
The process starts when the nucleus of uranium 235 atom absorbs a neutron
This makes the nucleus unstable Mir splits into two parts and releases a number of neutrons
A large amount of energy is released
What happens once fission has started?
The process keeps itself going
Some of the neutrons that are produced by splitting nuclei go on to be absorbed by other uranium nuclei
This process continues making it a chain reaction
What is nuclear fusion?
Is when the nuclei of small atoms join together to make larger atoms
This is very hard to achieve but is possible within a star where the gravitational forces can force the nuclei together
It’s difficult as the nucleus of an atom is positively charged and any two nuclei will always repel each other
What are control rods?
They absorb neutrons
Move in and out of the nuclear fuels to control the speed of nuclear reactions
What is used in nuclear fuel?
Either uranium 255 of plutonium 239 as they are more likely to undergo nuclear fission
