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PHYSICS GCSE P4

QuestionAnswer
An atom consists of a what charged nucleus, surrounded by an equal number of negatively charged electrons? A positively charged nucleus
In a stable, neutral atom, are the positive and negative chargers the same amount? Yes
An atom has four electrons, how many protons does it have? 4
When a polythene rod is rubbed with a duster, electrons are transferred from the duster onto the polythene. Does this make it negatively charged or positively charged? Negatively charged
Why does an acetate rod become positively charged when rubbed with a duster? Electrons are moved from the acetate rod to the duster
What happens when a) acetate rods are brought together? b) polythene rods are brought near each other a) they repel - like charges repel- b) they attract - unlike charges attract-
When sparks occur from electricity, or there is an explosion, what does this mean there is present? Flammable gases, high concentration of oxygen
What is a current? The rate of flow of charge
Statis electricity is when dust is attracted to insulators like tv, or when materials cling to the body. Is this dangerous? No
How can electric shocks be avoided? (2 things) - a build up of charge can be earthed when the flow is connected to the earth - factories are at risk when machines become charges, so workers stand on rubber mats, so the charge cannot flow through them to earth
Why must a mobile phone not be used in a petrol station? A spark from the static electricity could ignite the flammable gases in the air
Suggest how tumble drier sheets can reduce static 'cling' in your clothes? The sheets contain oil so they reduce friction (fewer electrons transferred) . They are made from conduction material so charge cannot build up.
What is defibrillation? A procedure to restore regular hearth rhythm by delivering an electric shock through the chest to the heart
Suggest why the paddles of a defibrillator must be placed firmly on the bare chest? To ensure good electrical contact
What is the formula for calculating the power of a defibrillator? Power = energy / time
A shock from a defibrillator supplies 400J. It is switched on for 5 milliseconds (0.005), what is the power? Power = 400 / 0.005 = 80 000 W
Is the nozzle of a spray painter positively or negatively charged? Positively
Explain why you get a better finish if you earth a bicycle frame when spray painting. Electrons flow to or from earth to keep the frame uncharged giving a more even coverage. There is less waste.
What removes harmful particles from chimneys in factories? A dust precipitator
What charge is a metal grid/wires given from a high voltage supply? Negative
Why do the wires in an electrostatic dust precipitator need to be at a high voltage? To charge the soot particles when they come near the wires
What is an electric current? It is the flow of electric charge
Charge is carried by _______ charged electrons Negatively
What is current measured in and using what Measured in amperes (A) using an ammeter
What changes the resistance? A variable resistor
What is resistance measured in" Ohms
What is the formula for resistance? Resistance = potential difference / current
The pd (potential difference) across a resistor is 4.0V when the current through it is 0.5A. What is its resistance? 4 / 0.5 = 8 ohms
What is the live wire in a plug used for? It carries high voltage around the house
What colour is the live wire and where is it positioned? It is brown and it to the right
What is the neutral wire used for? It completes the circuit, providing a return path
What colour is the neutral wire and where is it positioned? It is blue and is the top wire
What it the earth wire used for? It is connected to the case of an appliance to prevent it becoming live
What colour is the earth wire and where is it positioned? It is green and it to the left
Calculate the current in a 10 ohm resistor when the pd across it is 4V 0.4 A
What is the formula to find the potential difference? V = IR
What is the formula to find the current ? I = V / R
Explain how a fuse protects an appliance Wire in a fuse melts if the current becomes too large, breaking the circuit and preventing overheating
How is sound produced? By vibrating particles that form a longitudinal wave
Finish sentences: the features of longitudinal sound waves are: 1) they can't travel through a ___The ___the medium, the ___ a wave travels 2) the higher the ___ or pitch, the ___ the wavelength 3) the louder the___the more ___ is carried by the wav 1) vacuum , dense , faster 2) frequency , smaller 3) sound , energy
What is ultrasound? Sounds which have too high a frequency for humans to hear (above 20 kHz)
What happens to the particles in a longitudinal wave? The vibrations of the particles are in the same direction as the wave
What happens to the particles in a transverse wave? The vibrations of the particles are at right angles to the direction of the wave
How is ultrasound used to break down kidney stones? A high-powered ultrasound beam is directed at the kidney stones, which breaks the stnes down to smaller pieces. The tiny pieces are then excreted from the body.
Body fat is denser than air. I which medium will ultrasound travel faster? Body fat
Is a Mexican wave a transverse or longitudinal wave? Transverse
In body scans, When ultrasound is reflected from different parts of the body the depth of each structure is calculated by what formula? Distance = speed x time
Why is ultrasound preferred to x-ray? It differentiates between soft tissues better It doesn't damage living cells
An ultrasound pulse travels 20cm further when it is reflected from one side of the head of a foetus compared to the other side. How big is the head? 10cm
The time delay for an ultrasound echo in a soft tissue was 0.0004 seconds. At what depth was it reflected if the speed of ultrasound in th soft tissue was 1200m/s? 0.0004 x 1200 = 0.48 0.48 / 2 = 0.24
What are the three types of radiation? Alpha , beta , gamma
How are they emitted? From the nucleus of an unstable atom
Describe alpha Absorbed by the skin so not useful for diagnosis/therapy
Describe beta Passes through skin, but not bone. Medical applications are limited for example used to treat the eyes
Describe gamma Very penetrating and is used in medicine. Cobalt-60 is a gamma emitting material which is used to treat cancers.
REMEMBER GAMMA - Greatest
When nuclear radiation passes through a material is causes_____ Ionisation
What is radiotherapy ? When cancer cells are destroyed by exposing the affected area to large amounts of radiation.
Give 2 similarities and 2 differences between x-rays and gamma rays Similarities 1 both have very small wavelength 2 both damage or kill living cells Differences 1 x-rays are easy to control, gamma rays are not 2 gamma rays can sterilise equipment
What happens to the nucleus of an atom of a radioactive substance when it decays? It emits an alpha or a beta particle, losing any surplus energy by emitting gamma rays
What is a radioactive tracer used for? To investigate inside a patients body without surgery
Why is iodine-123 used as a tracer in medicine? Iodine is taken up by the thyroid gland and it emits only gamma radiation
A ______ is used to destroy a tumour in the body Radioisotope
Explain why gamma radiation is often directed at a tumour from several different directions? So that the tumour recieves full dose of radiation but healthy tissue recieves less radiation
Radioactive substances decay naturally, giving out what? Alpha, beta and gamma radiation
What is an isotope? One of two or more atoms having the same atomic number but different mass numbers
Three successive measurements of the activity of a radioactive source are 510Bq, 495Bq, and 523Bq. Why are they different? Radioactive decay is a random process
The activity of a radioactive sample took 8 hours to decrease from 5000Bq to 1250Bq. What is its half life? 4 hours
What is half life? The time taken for half the nuclei present to decay
What are the properties of alpha and it's nuclear equation for decay? Positively charged, Has a large mass, Helium nucleus with helium gas surrounding it, Consists of 2 protons and 2 neutrons 238 234 4 U ---> Th + He(alpha particle) 92 90 2
What are the properties of beta and it's nuclear equation for decay? Negatively charged, has a very small mass, travels very fast, is an electron 14 14 0 C ---> N + e 6 7 -1
Complete the nuclear equation: 219 ___ 4 Rn ---> Po He 86 ___ 2 215 Po 84
What is the background radiation? Medical, radioactivity in air, food, rocks, radiation from space (cosmic rays)
2 things tracers are used for 1. Find leaks in underground pipes 2. Track dispersal of waste materials
Why can't carbon dating be used to find the age of an iron tool? Iron was never living so does not contain carbon-14
What is carbon-14 A radioactive isotope of carbon used in carbon-dating calculation
Why must gamma be used as a trace rather than an alpha or beta source? Only gamma radiation will penetrate through pipes, ground, etc
Why would you expect a new rock to contain a bigger proportion of uranium to lead than an old rock? There is more uranium and less lead than an old rock.
The half life of carbon-14 is 5600 years. Why can't it be used to date an object believed to be about 100 years old? Very little carbon-14 would have decayed so there would be very little change in activity
What happens when an object dies? No more carbon-14 is produced
As the carbon-14 decays' the activity of the sample______ Decreases
Natural uranium consists of 2 isotopes, which are? Uranium-235 and uranium-238
Describe the steps of a chain reaction 1) a neutron is absorbed by the nucleus of a uranium-235 atom 2) the nucleus is now less stable than before 3) it splits in 2 parts and releases energy 4) several atoms produced, may go on to strike the nuclei of other atoms causing further fission
What is meant by 'enriched uranium'? Uranium containing a greater proportion of the uranium-235 isotope than occurs naturally
What is a chain reaction? A reaction where the products cause the reaction to go further and faster
How is very low level, low level and high level waste disposed of? Very low: placed in a sealed plastic bags then buried/burned under strict controls Low: embedded in glass disc and buried in the sea High: reprocessed to make more radioactive materials
Why is radioactive waste dangerous? It emits harmful ionising radiation for a long time
What do the control rods do in a nuclear reactor? They absorb some of the neutrons to control the number of fissions occurring
Created by: Lowri