Section 6 - Fields Exam Questions Flashcards
Explain what is meant by the gravitational potential at a point in a gravitational field (2)
Work done against the field per unit mass, when moved from infinity to the point
State Newton’s law of gravitation (2)
Force of attraction between two point masses is proportional to the product of the masses and inversely proportional to the square of the distance between them
Cavendish’s experiment to test Newton’s law of gravitation involved two unequal sized lead spheres, describe and explain the effect of doubling the radii on the force (3)
For the spheres mass is proportional to volume
Mass of either sphere would be 8x greater
This makes the force 64x greater
But separation would be doubled causing force to be 4x smaller
Net effect would make the force 16x greater
Describe the properties of the geostationary orbit and the advantages it offers for communications satellites (5)
Orbits westwards over the equator
Maintains a fixed position relative to surface of Earth
Period is 24 hours
Offers uninterrupted communication between transmitter and receiver
Steerable dish not necessary
Describe and explain what happens to the speed of a satellite in geostationary orbit when it moves in orbit closer to Earth (2)
Speed increases
Loses potential energy but gains kinetic energy
Why would geo stationary satellites not be suitable for use in tracking road vehicles? (2)
Signal would be too weak at large distance
Signal spreads out more the further it travels
Give two points in arguing for or against tracking road vehicles and explain (4)
Road pricing would reduce congestion
Road pricing would increase cost of motoring
Stolen vehicles can be tracked and recovered
Possibility of state surveillance
What is the SI unit of gravitational potential?
Is it vector or scalar? (1)
J/kg
Scalar
What is the SI unit of electric field strength?
Is it vector or scalar? (1)
V/m
Vector
Define electric field strength at a point in an electric field (2)
Force per unit charge
Acting on a positive charge
A flash tube in a camera produces a flash of light when a capacitor is discharged. State and explain the effect on the photograph image of a moving object if a capacitor of greater capacitance is used (4)
Image would be less sharp because the discharge would last longer and the image would be photographed as it is moving
Image would be brighter because the capacitor stores more energy and therefore produces more light
Give two reasons why a capacitor is not a suitable source for powering a cordless phone (2)
Capacitor would be too large to fit in phone
Capacitor would need charging very frequently
A student had to design an experiment to measure the acceleration of a heavy cylinder as it rolled down an inclined slope of constant gradient. They used a capacitor discharge circuit to measure time taken to travel between two points on the slope.
Describe the procedure and include measurements to be made and how to calculate acceleration (6)
Initial pd across C(V0) from voltmeter before releasing roller
Distance s along slope between plungers
Final pd across C(V1) from voltmeter
Measurements to be repeated for a more reliable result
Time t found from V1 = V0 x e^(-t/RC)
From s=ut + 0.5at^2
Repeat and find average a from several results
Describe the trajectory of charged particles entering at right angles to a uniform electric field (1)
Parabolic
Describe the trajectory of charged particles entering at right angles to a uniform magnetic field (1)
Circular
Which quantities out of mass (m), charge (Q), magnetic flux density B with a speed v, if changed would affect the radius of the circular path? (1)
All four
Give the units of all quantities in F=BIl (1)
F - N
B - T
I - A
l - m
Under what conditions does F=BIl apply? (1)
I (current) must be perpendicular to B
If a 2+ copper ion is projected from the left into a magnetic field that is directed upwards, in what direction will the magnetic force act on the ion? (1)
Out of the plane of the diagram
If a 2+ copper ion is into a magnetic field, what is the effect on the ion’s path if the strength of the magnetic field is doubled? (1)
Radius halved
If a 2+ copper ion is projected into a magnetic field, what is the effect on the ion’s path if the ion is replaced by a 1+ ion instead? (1)
Radius doubles