Physics P4 GCSE

Frage	Antworten
P4 What does an atom consist of?	It consists of a small positively charged nucleus surrounded by an equal number of negatively charged electrons.
P4 What is in a stable neutral atom?	The same amounts of positive and negative charges.
P4 What are all electrostatic effects due to?	All electrostatic effects are due to the movement of electrons.
P4 What does the law of electric charges state?	Like charges repel and unlike charges attract.
What happens when a polythene rod is rubbed with a duster?	When a polythene rod is rubbed with a duster electrons are transferred from the duster to the polythene, making the polythene rod negatively charged.
P4 What happens when an acetate rod is rubbed with a duster?	When an acetate rod is rubbed with a duster electrons are transferred from the acetate to the duster, making the acetate rod positively charged.
P4 What do anti-static sprays, liquids and cloths made from conducting materials do?	Anti-static sprays, cloths and liquids made of conducting materials carry away electric charge to prevent a charge build up.
P4 In general what does an object have?	In general an object has a negative charge due to an excess of electrons and a positive charge due to a lack of electrons.
P4 What does a dust precipitator do?	Dust precipitators remove harmful particles factory and power stations that pollute the atmosphere.
P4 What are ions?	Atoms or molecules that have become charged are ions.
P4 What is placed in chimney's and how does it get rid of the harmful particles?	A metal grid of wires is placed in a chimney and given a large charge from a high-voltage supply. Plates inside the chimney are earthed and gain an opposite charge to the grid. The dust particles go near the grid and become charged with the same charge as the grid. As like charges repel the dust is repelled from the wires and attracted the oppositely charged plates and stick to them. The plates sometimes vibrate and the dust falls onto a collector. (to become charged the dust particles gain or lose electrons. The dust particles charge induces a charge on the earthed metal plate.)
P4 What could cause an explosion?	If an inflammable gas or vapour is present or if there's a high concentration of oxygen a spark from static electricity could ignite these gases and vapours and cause an explosion.
P4 Describe how static electricity is used in spray painting.	When spray painting static electricity is used by the spray gun being charged. All the paint particles also become charged with the same charge. Like charges repel so the paint particles spread out giving a fine spray. That object that's about to be painted is given the opposite charge to the paint. Unlike charges attract so the paint sticks to the object due to being attracted. Limited paint is wasted and the object gets an even coat.
P4 What happens if a person touches something with high voltage?	Large amounts of electric charge may flow through their body to Earth if they touch an object with high voltage.
P4 What happens if the object to be painted is not charged and why is this bad?	If the object isn't charged the paint particles will still move onto it and charge the object. The object will gain the same charge. Further paint droplets are repelled from the object meaning paint is wasted and the charge isn't even.
P4 Can small amounts of charge flowing through the body be fatal?	Yes.
P4 If the paint is negatively charged what should the object be?	If the paint is negatively charged (gain electrons) the object should be positively charged (lose electrons) as unlike charges attract. The object must be the opposite charge to the paint.
P4 What are some examples of static electricity that isn't dangerous?	Dust and dirt are attracted to insulators like tv screens. Synthetic material clothes often cling to each other and the body.
P4 How can electric shocks be avoided?	If an object that's likely to be charged is connected to Earth, charge build up would immediately go down the Earth wire. Operators in factories where machines may become charged stand on insulating rubber mats so charge can't flow through them to Earth. Workers may also wear shoes with insulating soles so charge can't flow through them to Earth. Conducting cables connect fuel tankers to an air craft during refuelling.
P4 What is defibrillation? Describe the process.	An electric shock is delivered to the heart through the chest wall by the defibrillator to restore the hearts regular rhythm. Process A high voltage supply charges two paddles. To ensure good electrical contact they're placed firmly on the patient's chest. To make the heart contract electric charge is passed through the patient. Great care should be taken so that the operator doesn't receive an electric shock.
P4 What things or factors can change resistance?	A variable resistor or rheostat can change the resistant. \factors like longer wire length or thinner wires means more resistance.
P4 Describe voltage and how it can affect current.	Voltage is measured in volts using a voltmeter connected in parallel. For fixed resistors as the voltage increases the current increases. For a fixed power supply as the resistance increases the current decreases.
P4 Describe the three types of wires.	Live wires carries a high voltage around the house. Neutral wire completes the circuit. It provides a return path for the current. Earth wire is connected to the appliances case to prevent it becoming live.
P4 Describe fuses and why they're positive?	A fuse contains a wire that melts and breaks the circuit when the current becomes too large. The current is unable to flow so overheating and further damage to the appliance is avoided.
P4 What happens if the case of an appliance becomes live?	When an appliance's case becomes live a large current flows in the earth and and live wires and fuse 'blows'. The earth and fuse prevents someone receiving an electric shock if they touch a faulty appliance.
P4 Can the power of an appliance be restored?	Yes, a resettable fuse (circuit-breaker) doesn't need to be replaced, it can be reset.
P4 What is power rating?	Power rating is the rate at which an appliance transfers energy.
P4 What can the formula power = voltage x current be used for?	To calculate the correct fuse to use in an appliance.
P4 Describe ultrasounds.	Ultrasound is above 20 000 Hz which is a higher frequency than humans can hear. It travels as a pressure wave containing compressions and rarefactions.
P4 What is a compression?	A region of high pressure with particles close together.
P4 What is a rarefaction?	A region of low pressure with particles widely spread apart.
P4 Describe the features of longitudinal sound waves.	They are unable to travel in a vacuum. Denser medium = sound wave travelling faster The higher the frequency or pitch the smaller the wavelength. Louder sound / more powerful ultrasound = wave carrying more energy and larger amplitude.
P4 Describe the difference between longitudinal and transverse wave vibrations.	Longitudinal wave vibrations of particles are parallel to waves direction. Transverse wave vibration of particles are at right angles to the direction of the wave.
P4 Describe how ultrasound breaks up kidney stones.	A high powered ultrasound beam is directed towards the kidney stones. The ultrasound energy breaks the stone down into smaller pieces. The smaller pieces are excreted out the normal way.
P4 Describe how an ultrasound is used in a body scan fully.	A pulse of ultrasound is sent into the body. At each boundary between different tissues some of the ultrasound is reflected while the rest is transmitted. Returning echoes are recorded and used to build up an image of the internal structure.
P4 Why can ultrasound be used for body scans?	When ultrasound is reflected from diff parts of the body the depth of each structure is calculated using d = s × t. We know the speed for the ultrasound of diff tissue types and the time for the echo to return. The density of the adjoining tissues and the speed of sound in the adjoining tissues reflect the proportion of ultrasound reflected at each interface. Very different tissues cause most of the ultrasound to be reflected so little penetrates further into the body. Info is gained to produce an image of the scanned body.
P4 Why is ultrasound preferred to x-rays?	Ultrasound can produce images of soft tissue. Ultrasound doesn't damage living cells.
P4 Describe radioactive substances	Radioactive substances decay naturally and emit alpha, beta and gamma radiation.
P4 What does nuclear radiation cause and how?	Nuclear radiation causes ionisation by removing electrons from atoms or making them gain electrons.
P4 Describe radioisotopes.	Radioisotopes have so many atoms that the avg count rate is always the same. They have unstable nuclei. The nuclear particles are not held strongly enough.
P4 What is the half life?	The halflife of a radioisotope is the avg time for half of the nuclei to decay. It can not be changed.
P4 How can the nucleus of an atom be represented?	a X z a = atomic mass z = atomic number (proton) a = z + neutrons
P4 How does an element change?	An alpha or beta is emitted from the nucleus of the atom so the remaining nucleus is a diff element.
P4 Describe alpha fully.	Good ioniser. Large particles emitted during radioactive decay. More likely to strike atoms of materials they pass through (ionising them). Positively charged. Large mass Helium nucleus Helium gas around it. 2 protons. 2 neutrons. Decay:: a -4. z -2. n -2n -2p.
P4 Describe beta particles fully.	Negatively charged. Small mass. Travels fast. Electron. Decay: a same. z +1 n -1n +1p
P4 What is background radiation due to?	Radioactive substances in rocks (especially granite). Cosmic rays from space. Man made sources like radioactive waste from industry and hospitals.
P4 Describe how a tracer is used to locate a leak in an underground pipe.	A small amount of gamma emitter (which can penetrate the surface) is put into the pipe. A detector is passed along the ground above the pipes path. In the region of the leak an increase of activity is detected. Little or no activity is detected after this point.
P4 Describe alpha particles in smoke detectors.	A smoke detector contains an isotope that emits an alpha particle. Normally the alpha particles ionise the air which produces a current that can be detected by the smoke alarm. With smoke the alpha particles are slightly blocked so the air is less ionised and the change in current is detected resulting in the alarm sounding.
P4 Describe rock types in terms of radioactive materials.	Some rock types like granite contain traces of radioactive substances like uranium. A stable isotope of lead is formed as the uranium isotopes go through a series of decays. Through comparing the amounts of uranium and lead in a rock sample it's age can be found.
P4 How do you know a rock is 4500 million years old?	The proportion of lead increases as time increases. If there are equal quantities of lead and uranium the rock is one half life old.
P4 What is carbon dating?	Carbon-14 is a radioactive isotope of carbon and is present in all living things. Measuring the amount of it present in something gives its approximate age. It can only be used on dead objects. No more carbon-14 is produced in dead animals. The carbon-14 decays and the samples activity decreases. An accurate date can be produced from the ration of current activity from living matter.
P4 What is background radiation due to?	Radioactive substances in rocks (especially granite). Cosmic rays from space. Man made sources like radioactive waste from industry and hospitals.
P4 List what we use radiation for.	Alpha radiation is absorbed by the skin and therefore not useful for diagnosis or therapy. Beta radiation passes through skin, but not bone so it's application is limited, but could be used to treat the eyes, Gamma radiation is very penetrating and used in medicine. Cobalt-60 is a gamma emitting radioactive material that is widely used to treat cancer.
P4 Describe ionisation fully.	Ionisation is when nuclear radiation passes through a material. It damages living cells and increases the risk of cancer.
P4 What is radiotherapy?	Radiotherapy is exposing cancer cells in the body with large amounts of radiation.
P4 How do you make materials radioactive?	When nuclei absorbs extra neutrons in a nuclear reactor the material is being made radioactive.
P4 What happens when X-ray passes through the body?	The tissues absorb some of the x-ray's ionising radiation. How much absorbed depends on the thickness and density of the absorbing material.
P4 Difference between x-rays and gamma?	They both have a similar wave length, but are produced in a different way.
P4 Describe x-rays and how they're made and how gamma radiation is different.	X-rays are made by firing high speed electrons at metal. An x-ray machine allows rate of production and energy .to be controlled. Gamma radiation emitted from a radioactive source can't be controlled.
P4 What happens when the nucleus of an atom of a radioactive substance decays?	An alpha or beta particle is emitted and surplus energy is lost by emitting gamma when the nucleus of a radioactive atom decays.
P4 Describe how a radioactive tracer is used to investigate inside a patients body.	The radioactive tracer is mixed in with food or a drink or injected into the body. It progresses through the body and is monitored using a detector like a gamma camera connected to a computer.
P4 What is a radioisotope used for in treatment and describe how.	It destroys as tumour in the body. This happens by three radiation sources providing 1/3 of the required dose and arranged around the patient with the tumour at the centre. The healthy tissue receives minimum damage due to receiving only 1/3. An alternative is that each radiation source is rotated around the patient. The tumour receives a constant dosage.

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