KEY FLASHCARDS FOR 4TH EOY

Question 1

what is half-life?

Answer 1

• half the time it takes for the radioactive sample to decay

Question 2

how can you identify the type of radiation?

Answer 2

• 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

Question 3

how to investigate radioactivity?

Answer 3

1. you can detect ionising radiation with a geiger muller detector
2. 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
3. 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
4. do this three times and find the mean and subtract from all your results
   5.

Question 4

what type of decay is radioactive decay?

Answer 4

• random decay

Question 5

what must be recorded first for finding radiation of sample?

Answer 5

• background radiation

Question 6

what are the risks of radiation and how do you dispose of it?

Answer 6

• ionising radiation can damage human cells and tissues
• DNA mutations -> cancer
• BURY UNDERGROUND TO PREVENT FROM BEING RELEASED INTO THE ENVIRONMENT

Question 7

radiation safety measures

Answer 7

• kept in a shielded container when not in use -> a lead lined box
• handle with tongs
• limited exposure

Question 8

what do you use to measure background radiation?

Answer 8

geiger muller tube
- count the clicks

Question 9

what is fission?

Answer 9

one large nucleus split into two smaller daughter nuclei

Question 10

what is fusion?

Answer 10

two small nuclei join together to form a larger nucleus

Question 11

what does fusion require and why?

Answer 11

• VERY HIGH / EXTREME TEMPERATURES AND PRESSURES TO ENABLE THEM TO OVERCOME THEIR ELECTROSTATIC REPULSION BETWEEN TWO NUCLEI TO FUSE TOGETHER

Question 12

importance of the parts of nuclear reactors

Answer 12

• 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

Question 13

state the equation linking voltage, current and resistance.

Answer 13

v = ir

Question 14

circuit practical to investigate v=ir

Answer 14

• need variable resistor to vary the voltage

Question 15

how does a fuse work?

Answer 15

• 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

Question 16

how do earth wire and fuse work together?

Answer 16

• 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

Question 17

graphs for different electical components

Answer 17

LEARN FROM CGP GUIDE

Question 18

state the equation linking power, energy transferred and time.

Answer 18

• power = energy transferred /time

Question 19

current in series vs current in parallel

Answer 19

• current is the same everywhere in series
• splits between the branches

Question 20

voltage in series vs voltage in parallel

Answer 20

• series -> different voltages
• parallel -> same in each branch

Question 21

what is the law of reflection

Answer 21

angle of incidence = angle of reflection

Question 22

practical for reflection

Question 23

practical for refraction

Answer 23

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

Question 24

total internal reflection

Answer 24

• occurs when the angle of incidence is greater than the critical angle and the incident material is denser than the second material

Question 25

how does total internal reflection look like on graph?

Question 26

oscilloscope practical to investigate sound waves

Answer 26

1. Connect the microphone to the oscilloscope as shown in the image above
2. Test the microphone displays a signal by humming
3. Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
4. Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
5. Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
6. Freeze the image on the oscilloscope screen, or take a picture of it
7. Measure and record the time period of the wave signal on the screen by counting the number of divisions for one complete wave cycle
8. Repeat steps 4-6 for a variety of tuning forks

Question 27

what is flemmings l.h rule

Answer 27

• point first finger in direction of field and second finger in direction of current
• thumb points in direction of force

Question 28

what is flemmings r.h. grip rule

Answer 28

• arrange thumb, index and middle perpendicular to each other
• thumb points towards direction of the motion of the conductor relative to the magnetic field
• forefinger points towards direction of magnetic field
• middle towards direction of induced current

Question 29

field lines around wire and solenoid

Answer 29

• straight wire : in the centre - > field lines around it
• flat circular coil -> similar to bar magnet -> concentric ellipses of magnetic field lines around coil
• solenoid -> outside the coil is just like a bar magnet

Question 30

describe a practical to figure out the direction and shape of the field lines.

Answer 30

METHOD 1: iron filings
1. trace bar magnet onto paper
2. place magnet under paper
3. sprinkle iron filings
4. tap page to reveal shape
METHOD 2: COMPASS
1. place paper on top of bar magnets
2. place plotting compass at one corner of the N-pole of the magnet
3. draw a dot where the compass is pointing
4. move the compass forward so that the tail is adjacent to the point you just plotted
5. draw another dot where the compass is pointing
6. continue until you reach the S-pole and connect the dots with a smooth curve
7. repeat steps 3-6 drawing multiple field lines around the magnet

Question 31

what will current going through wire reversed do?

Answer 31

• make magnetic field go in the opposite direction

Question 32

loudspeakers

Answer 32

• work because of the motor effect
• a.c electrical signals from an amplifier are fed to a coil of wire in the speaker -> wrapped around the base of a cone
• coil is surrounded by a permanent magnet -> a.c. signals cause a force on the coil and move it back and forth
• movements make the cone vibrate and creates sounds

Question 33

factors that will speed up motors

Answer 33

• more current
• more turns in the coil
• stronger magnetic field
• a soft iron core in the coil - solenoid