Everything you need to know for Edexcel Physics!

This is all for UNIT 1 Mechanics and Radioactivity

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Describe how you could check experimentally that momentum is conserved in a collision between two trolleys. (Past Paper 18th January 2001)
Friction is considered to be negligible throughout this experiment.
To begin, one must attach ticker tape to a trolley A of known mass. One must then apply a constant force to this trolley so that it travels at constant velocity and collides inelasticly with a stationary trolley B to which a separate ticker tape is attached. The ticker timer moves a metal pin up and down 50 times per second creating various dots on the paper tape which passes underneath. Therefore by cutting the ticker tape of trolley A into sections 10 dot spaces long, one can find the distance travelled by trolley A in 0.2 seconds (multiply by 5 to get the average velocity). Similarly one can find the combined velocity of trolley A and B after the collision. Momentum = mass x velocity, so if Mass of trolley A x Velocity of trolley A + Mass of trolley B x 0 = combined mass of trolley A and B x combined velocity then momentum has been conserved in this collision.

What is meant by the term half-life? (18th January 2001) (15th January 2004)
The half-life of a radioactive nuclide is the average time taken for the activity to halve.

State the principle of moments. (18th January 2001)
If an object is in equilibrium, the sum of the clockwise moments about any axis is equal to the sum of the anticlockwise moments.

How would a student determine the background radiation level in the laboratory? (18th January 2001)
In order to determine background radiation, one must set up a GM tube and counter making sure there is no source within 5metres. One then measures the counts in one minute ten times in a row and takes an average.

From these experiments explain how the student could confirm that the sample was a pure beta emitter. You may be awarded a mark for the clarity of your answer. (18th January 2001) also (14th January 2002)
To begin the student must place the radioactive element at a relatively small distance from the Geiger Muller tube in order to make sure that the emitted radiation count due to the sample is significant even after subtracting the background radiation.
He must then place this element half a meter away, if the value on the counter stays the same then no alpha radiation is being emitted. Finally the student must place the piece of aluminium between the element and the Geiger Muller tube, if the value on the count rate drops to the background radiation level then no gamma radiation is being emitted. The sample is therefore a pure beta emitter.

Complete the following table which compares alpha particle scattering and deep inelastic scattering experiments. (18th January 2001), (16th January 2003), (6th June 2003), (15th January 2004)
Alpha particle scattering:
Incident particles: Alpha particles Target: Thin gold foil
Deep inelastic scattering:
Incident particles: High energy Electrons Target: Nucleons

Write a short paragraph describing the conclusion from each experiment.
Alpha particle scattering
As most particles went straight through, undeflected one can conclude that most space in the foil must be empty occupied only by electrons. A tiny minority of alpha particles were deflected through either small or large angles due to the fact that the atom’s mass is mainly concentrated in a small positively charged nucleus.
Deep Inelastic scattering
From this experiment one can conclude that Protons have a structure and that there charge is not uniform but split between even smaller charged particles, the Quarks.

Alpha particle radiation has a short range in matter. With reference to the effect of alpha particles on atoms, explain why they only travel a short distance. (6th June 2001)
Alpha particles have a very short range in air (a few centimetres), and although they are the most ionising any collision with an atom will bring them to rest.

Suggest how you could demonstrate that the volume of water when heated from 0c to 10C behaves in the manner indicated by the graph. You may be awarded a mark for the clarity of you answer (6th June 2001)
Fill up a measuring cylinder with 1kg of water, using a digital balance and subtracting the mass of the cylinder to find a precise reading. Cool the water untill it freezes and then place the cylinder on top of a heat source, making sure to suspend a thermometer in the water using a ring stand and clamp. Allow the water to heat slowly writing down the volume at each degree Celsius. Finally plot a volume-temperature graph.
(The answer to this experiment is my personal work; therefore I would greatly appreciate if someone could post a better version).

Samples of two different isotopes of iron have been prepared. Compare the compositions of their nuclei. (14th January 2002) (15th January 2004)
Isotopes are nuclides with the same proton number but a different neutron number. They therefore share the same chemical properties but different physical properties.

The samples have the same chemical properties. Suggest a physical property which would differ between them.
They will have different atomic masses, and so have different densities.

State the composition of an alpha particle. (May 31st 2002)
An alpha particle is the nucleus of a helium atom and is made up of two protons and two neutrons.

When an alpha particle passes through matter, it may ionise atoms. Explain what ionise means.
Ionising radiation has the ability to strip off electrons from atoms or molecules in its path.

A beta particle from a different radioactive source has the same kinetic energy as the alpha particle. Explain qualitatively how the speed of this beta particle would compare with the speed of the alpha particle.
Beta particles are much lighter than alpha particles; therefore in order for them to have the same amount of kinetic energy (1/2mv2), there speed must be far greater.

Beta particles are many times less effective at ionising atoms than alpha particles. Suggest a reason for this.
Beta particles contain less charge and spend less time in the atom due to their huge speeds; this might explain why they are far less ionising.

Initially two trolleys are at rest, in contact, on a horizontal bench. A spring-loaded piston is then released in one trolley, pushing the trolleys apart. Describe an experimental technique by which you could determine accurately the speeds of the trolleys after they separate. (31st May 2002)
To begin, one must attach separate ticker tapes to each individual trolley. The ticker timer, which has been connected to the tape, moves a metal pin up and down 50times per second creating various dots on the paper tape which passes underneath. Therefore by cutting the ticker tape into sections 10 dot spaces long, one can find the distance travelled by each trolley in 0.2 seconds, (multiply by 5 to get) the average velocity just after the trolleys separate.

Explain two precautions, other than safety precautions, which the student should take in her measurements in order to produce a reliable value for the half-life. (31st May 2002)
The student must repeat the count several times and take an average, as radioactive decay is a random process. She must also subtract the background radiation and make sure the source is at the same distance from the Geiger Muller tube each time she takes a reading.
Which nucleus in the list is likely to produce the densest material? (31st May 2002)
The nucleus with the biggest mass number will produce the densest material.

State Newton’s Second Law of motion. (16th January 2003)
Resultant force in Newton’s = Mass in kg x Acceleration in ms-2

Describe, how you could demonstrate experimentally that the acceleration of a trolley is proportional to the resultant force, which acts on it. (16th January 2003)
To begin one must set up a runway and tilt it just enough so that a trolley runs down it at constant speed when given a push this ensure that force of friction is balanced out. One may then use a forcemeter to apply a constant force to the trolley, which has been attached to ticker tape. As the trolley accelerates down the incline the ticker timer moves a metal pin up and down 50times per second creating various dots on the paper tape which passes underneath. Therefore by cutting the ticker tape into sections 10 dot spaces long, one can find the distance travelled by the trolley in 0.2 seconds. These measurements will provide the average speeds u and v separated by a time t1. The acceleration a is then given by (v-u)/t1, once found we vary the force and plot a force – acceleration graph if it is a straight line going through the origin then the acceleration of a trolley is proportional to the resultant force.

Suggest what Geiger and Marsden would have observed if the “plum pudding” model had been correct.
(16th January 2003)
If the plum pudding model had been correct most alpha particles would have gone straight through the atom, as there is no dense object to collide with.

The acceleration of free fall g can be measured by timing an object falling from rest through a known distance. Explain one advantage and one disadvantage of making this distance as large as possible. (6th June 2003)
Advantage: The time it takes the object to fall will be bigger, it is therefore easier to measure accurately and % error is less significant.
Disadvantage: Friction due to air resistance will play a more important role for a larger distance.

In a typical laboratory measurement of g, a steel sphere is dropped through a distance of the order of one metre. With the help of a labelled diagram, describe and explain an experimental method of measuring the time is takes the sphere to fall.

Initially, when the switch is in position A the steel ball is held by an electromagnet thus allowing us to measure the distance x from the bottom of the ball to the top of the trapdoor. We may then switch to position B, the electromagnet will release the ball, the clock circuit will be completed and the clock will start. When the ball hits the trapdoor it opens the clock circuit and the clock stops. We may then record the time t that the ball has taken to fall.

At any given place, the weight of a body is proportional to its mass. Explain how measurements of g support this statement.
By measuring acceleration for various objects we find it is constant at a given place. Therefore W/M is constant which means that the weight is proportional to the mass.

Background count rate (6th June 2003): 0.3 - 05 Bq

Radioactive decay is a random process. Explain what this means (15th January 2004)
Radioactive decay is a random process; there is no way of predicting, when a particular nucleus will decay.
Complete the table below by giving on example of each type of force. (14th June 2004)
Gravitational: The gravitational force that a planet applies to a body is called its weight. When you are standing on the Earth, the earth pulls you towards it.
Electromagnetic: Between two magnets, or between a magnet and another piece of magnetic materiel.
Nuclear: The weak nuclear force is involved in beta decay when a neutron decays to a proton, with the emission of an electron.

State three properties of these forces which are necessary for them to be a Newton’s third lay pair.
Forces in a Newton’s third law pair have the same line of action, act for the same amount of time, are of the same type, and are always equal and opposite.

A student measures the background radiation in a laboratory at 4.0 Bq. State two sources of background radiation. (6th June 2001)
Background radiation is partly due to rocks, cosmic radiation, nuclear power stations and the soil.

Describe an experiment she could perform to find out what percentage of the gravitational potential energy lost is actually converted to kinetic energy. (14th June 2004)

To begin the physics teacher must fix a card of known length to a trolley of known mass (m) so that it interrupts a light beam. She must then measure the initial gravitational potential energy of the trolley at the top of the runway using the formula GPE=mgh. She may then release the trolley to roll down the slope. With the help of the light gate the teacher can determine the speed of the trolley as it reaches the end of the runway and therefore deduce a value for the amount of kinetic energy gained by the trolley ( 1/2mv^2). She can then divide the value found for gained KE by the value found for initial GPE and multiply it by 100% to find out what percentage of the GPE was successfully converted into KE.

This isotope of polonium is thought to emit only alpha radiation. Describe how you could check this experimentally. (14th June 2004)
To begin the student must place the radioactive element at a relatively small distance from the Geiger Muller tube in order to make sure that the emitted radiation count due to the sample is significant even after subtracting the background radiation.
He must then place this element half a meter away if the value on the count rate drops to the background radiation level then only alpha radiation was being emitted.

State and explain the qualitative relationship between range and ionising ability. (14th June 2004)
The number of ion pairs the sample produces determines the range of the radioactive source; each ion pair requires the particle to do a fixed amount of work. So the initial kinetic energy of each particle will establish how many ions it can produce and how far it can go. To conclude if the radioactive element has a strong ionising ability it will have a small range, this is the case of alpha radiation. If instead the sample has a weak ionising ability it will have a bigger range, this is the case of beta and gamma radiation.

A trolley is released from rest at the top of an inclined plane. A student claims that the acceleration of the trolley should be uniform. Describe how you could test this claim experimentally. (17th January 2005)
As the trolley accelerates down the inclined plane, the ticker timer moves a metal pin up and down 50times per second creating various dots on the paper tape which passes underneath. Therefore by cutting the ticker tape into sections 10 dot spaces long, one can find the distance travelled by the trolley in 0.2 seconds, the average velocity (by multiplying by 5). If we plot a velocity (using the average velocity for each point two seconds) against time graph, and it is a straight line going through the origin then acceleration is uniform.