Physics Paper 2 Mistakes Flashcards
Explain what is meant by a capacitance of 120uF
Capacitor stores 120uC of charge for each volt of pd between the plates
What happens to capacitance if the dielectric is removed
Er decreases and capacitance decreases
What remains constant and what changes when the power supply remains connected (capacitance)
V constant
Q decreases
What remains constant and what changes when the power supply is disconnected (capacitance)
V increases
Q constant
Explain what is meant by ionisation
When an atom loses an electron
Discuss the energy transfers that take place in the accelerator as the ion passes through it
Potential energy of the ion is transferred to KE of ion.
Power supply transfers energy to the ion.
Decrease in energy stored in supply = increase in KE stored by ion
Discuss how the path changes when an ion enters the velocity selector with a velocity greater than v
The electric force is constant.
F = BQv and since B and Q are constant, F is directly proportional to v
When velocity increases, the magnetic force acting on the ion increases.
Ion accelerates in the direction of the force (state the direction of force using Flemings rules)
Ions created in the ioniser may have the same charge but a different number of nucleons.
Discuss how the path of an ion in the mass separator is affected when it has more nucleons
Bqv = mv^2 / r
r = mv / Bq
v, B, q are constant to r is directly proportional to m and so r increases
An alpha particle is targeted towards a gold nucleus with 79 protons.
The target nucleus is changed to one with fewer protons. The alpha particle is given the same initial KE.
Explain any changes that occur to the distance r.
R gets smaller.
Less force so needs to travel further to lose same initial KE.
Define gravitational potential at a point
Work done per unit mass in moving an object from infinity to a point
Explain why gravitational potential is always negative
Gravitational potential is defined as 0 at infinity.
(Forces are attractive) so work must be done on the mass to reach infinity therefore it is negative.
Describe and explain 2 features of a geostationary orbit
Time period of 24 hours.
In the plane of the equator.
Always above the same location on Earth
Explain the purpose of the core in the transformer
Core focuses/directs the magnetic field round to the secondary coil
Describe and explain 2 features of the core that improve the efficiency of the transformer
Made from soft iron so easily magnetised/demagnetised
The core is laminated to reduce eddy currents
Explain why transformers only work continuously when supplied with an alternating current
So there is a constant change in flux in the core
A pump can circulate the water at different speeds. When working at higher speeds the rise in temperature is greater.
Explain why.
When the pump is working at speed, the pump is doing work on the water.
Work can raise the temperature of a body.
Mean KE is proportional to temperature
Position P is on the line joining the charges at a distance of 66mm from a positive charge Q.
The resultant electric field strength at position P is zero.
Explain whether net work must be done in moving a proton from infinity to P
Work must be done to overcome electrostatic repulsion between the two positive charges.
The potential at infinity is zero.
Potential at P is positive
Lenz’s law can be demonstrated using a bar magnet and a coil of wire connected to a sensitive ammeter.
The bar magnet is moved towards the coil and is then brought to a halt.
State how the reading on the ammeter changes during this process
Reading shows a dc current flow which then becomes zero when the magnet stops moving.
Lenz’s law can be demonstrated using a bar magnet and a coil of wire connected to a sensitive ammeter.
During the demonstration an induced current is detected by the ammeter. The induced current is in the direction E to F. Explain how this demonstrates Lenz’s Law
Induced current produces a N pole on the right hand side of the coil, which opposes the motion of the bar magnet
Explain why the public need not worry that the irradiated surgical instruments become radioactive once sterilised
To become radioactive the nucleus has to be affected however sterilising the instruments does not affect the nucleus
State two possible reasons why the results do not follow the expected inverse square law
- The radioactive source is not a point source.
- Source may not be a pure gamma emitter
A nucleus of the stable isotope Pb-208 has more neutrons than protons.
Explain why there is this imbalance between proton and neutron numbers by referring to the forces that operate within the nucleus. Your explanation should include the range of the forces and which particles are affected by the forces.
Strong nuclear force (SNF) affects nucleons or protons and
neutrons.
SNF is attractive up to 3 fm (allow 1–4 fm)
The SNF is repulsive below 1 fm and prevents the nucleus totally collapsing
Electrostatic repulsive force (only) acts between protons
More neutrons are needed to hold nucleus together /increase instability/reduce stability
Fewer protons are required so as to reduce the repulsion §/increase stability
The thallium nucleus is formed in an excited state. Electromagnetic radiation is emitted from the thallium atom following its formation.
Explain the origin and location of two sources of this radiation.
Orbiting electrons in the atom fall (to fill the positions vacated by inner orbiting electrons releasing their energy as em (gamma) radiation
The excited nucleus emits gamma radiation (as it de-excites)
Other nuclides also emit electromagnetic radiation.
Explain why the metastable form of the isotope of technetium 43Tc 99 is a radioactive source suitable for use in medical diagnosis.
It only emits Gamma-rays.
Gamma-rays are weakly ionising so cause less damage to body than other radiations.
Gamma-rays can penetrate/escape from the body.
Half-life is short enough not to remain in the body for too long after the medical examination.
Half-life is long enough to complete the diagnosis.
It can be prepared in the hospital/close to the hospital.
