Section 6 - Fields Exam Questions Flashcards Preview

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Flashcards in Section 6 - Fields Exam Questions Deck (53)
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1

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

2

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

3

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

4

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

5

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

6

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

7

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

8

What is the SI unit of gravitational potential?
Is it vector or scalar? (1)

J/kg
Scalar

9

What is the SI unit of electric field strength?
Is it vector or scalar? (1)

V/m
Vector

10

Define electric field strength at a point in an electric field (2)

Force per unit charge
Acting on a positive charge

11

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

12

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

13

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

14

Describe the trajectory of charged particles entering at right angles to a uniform electric field (1)

Parabolic

15

Describe the trajectory of charged particles entering at right angles to a uniform magnetic field (1)

Circular

16

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

17

Give the units of all quantities in F=BIl (1)

F - N
B - T
I - A
l - m

18

Under what conditions does F=BIl apply? (1)

I (current) must be perpendicular to B

19

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

20

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

21

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

22

The magnetic flux through a coil of N turns is increased uniformly from zero to a maximum value in a time t. An emf, E, is induced across the coil. What is the maximum value of the magnetic flux? (1)

Et/N

23

How can a magnetic flux against time graph be transformed into an emf against time graph? (1)

Δφ/Δt = emf

24

Why are high voltages and low currents used when transporting electricity on the National Grid? (1)

Heat losses are reduced

25

A coil is connected to a centre zero ammeter, a student drops a magnet through the coil (North at the bottom).
Describe what the ammeter would show as the magnet falls through (2)

Deflects one way
Then the other way (after halfway through)

26

State and explain how the acceleration of the magnet would be affected as it entered the coil (2)

Acceleration is less than g
Lenz’s law

27

A magnet is passed through a coil connected to a voltmeter. Using Faraday’s law, explain why a larger emf would be induced if a stronger magnet moved at the same speed (3)

Greater flux linkage
Greater rate of change of flux linkage
Emf is proportional to rate of change of flux linkage

28

State what is meant by root mean square voltage (1)

The square root of the mean of the squares of all the values of the voltage in one cycle

29

State and explain the effect on the oscilloscope trace if the time base is switched off (2)

Vertical line is formed
Of length equal to twice the peak voltage
Because trace no longer moves horizontally

30

An alternating current supply provides an output voltage of 12 V rms at a frequency of 50 Hz. Describe how you would use an oscilloscope to check the accuracy of the rms output voltage and the frequency of the supply (6)

Power supply connected to oscilloscope input
Time base initially switched off
Y gain adjusted to get as long a line as possible
Length of line used to find peak to peak voltage
Rms voltage found
Time base switched on and adjusted to get several cycles on the screen
Use the time base setting to find period
Use period to find frequency
Compare values with stated values