KEY FLASHCARDS FOR 4TH EOY
what is half-life?
- half the time it takes for the radioactive sample to decay
how can you identify the type of radiation?
- by its penetration
- alpha is blocked by paper, skin or a few cm of air
- beta blocked by thin aluminium
- gamma rays blocked by thick lead
how to investigate radioactivity?
- you can detect ionising radiation with a geiger muller detector
- set up the equiptment with the source kept 2m away from the material and then the geiger muller tube away from that when nothing is placed between the source and detector, the counter records a high count rate
- remove the source to measure the background count over a time period and divide your count by the time period get a background count rate
- do this three times and find the mean and subtract from all your results
5.
what type of decay is radioactive decay?
- random decay
what must be recorded first for finding radiation of sample?
- background radiation
what are the risks of radiation and how do you dispose of it?
- ionising radiation can damage human cells and tissues
- DNA mutations -> cancer
- BURY UNDERGROUND TO PREVENT FROM BEING RELEASED INTO THE ENVIRONMENT
radiation safety measures
- kept in a shielded container when not in use -> a lead lined box
- handle with tongs
- limited exposure
what do you use to measure background radiation?
geiger muller tube
- count the clicks
what is fission?
one large nucleus split into two smaller daughter nuclei
what is fusion?
two small nuclei join together to form a larger nucleus
what does fusion require and why?
- VERY HIGH / EXTREME TEMPERATURES AND PRESSURES TO ENABLE THEM TO OVERCOME THEIR ELECTROSTATIC REPULSION BETWEEN TWO NUCLEI TO FUSE TOGETHER
importance of the parts of nuclear reactors
- in a nuclear reactor - chain reactions are needed to keep the reactor running
- control rods: absorb neutrons to reduce the number of free neutrons in the reactor
- moderators: to slow down neutrons -> made of graphite -> to control the energy of the free neutrons
state the equation linking voltage, current and resistance.
v = ir
circuit practical to investigate v=ir
- need variable resistor to vary the voltage
how does a fuse work?
- If the current exceed the fuse rating (sure in current)
the fuse wire heats up and melts - This breaks the circuit and isolate the appliance protecting it from overheating/fire
how do earth wire and fuse work together?
- The Earth wire is connected to the metal casing of the appliance
- if the live wire works loose (fault) and touches the metal casing
- there is a surge in current through to the Earth wire
- this melts the fuse wire
- isolating the appliance
- preventing an electric shock
graphs for different electical components
LEARN FROM CGP GUIDE
state the equation linking power, energy transferred and time.
- power = energy transferred /time
current in series vs current in parallel
- current is the same everywhere in series
- splits between the branches
voltage in series vs voltage in parallel
- series -> different voltages
- parallel -> same in each branch
what is the law of reflection
angle of incidence = angle of reflection
practical for reflection
practical for refraction
Place the glass block on a sheet of paper, and carefully draw around the block using a pencil
Draw a dashed line normal (at right angles) to the outline of the block
Use a protractor to measure the angles of incidence to be studied and mark these lines on the paper
Switch on the ray box and direct a beam of light at the side face of the block at the first angle to be investigated
Mark on the paper:
A point on the ray close to the ray box
The point where the ray enters the block
The point where the ray exits the block
A point on the exit light ray which is a distance of about 5 cm away from the block
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a rays striking the block at the next angle
total internal reflection
- occurs when the angle of incidence is greater than the critical angle and the incident material is denser than the second material
