Flashcards in Fields Exam Questions Deck (52)

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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 as total energy must remain constant.

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

##
What is the SI unit of gravitational potential?

Is it vector or scalar? (1)

###
J/kg

Scalar

8

##
What is the SI unit of electric field strength?

Is it vector or scalar? (1)

###
V/m

Vector

9

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

###
Force per unit charge

Acting on a positive charge

10

## 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

11

## 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

12

##
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

13

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

### Parabolic

14

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

### Circular

15

## 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

16

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

###
F - N

B - T

I - A

l - m

17

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

### I (current) must be perpendicular to B

18

## 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

19

## 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

20

## 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

21

## 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

22

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

### Δφ/Δt = emf

23

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

### Heat losses are reduced

24

##
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)

25

## 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

26

## 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

27

## 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

28

## 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

29

## 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

30