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PHYSICS GCSE P4
| Question | Answer |
|---|---|
| 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
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