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
