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RSFC Physics > Section 6 - Fields > Flashcards

Section 6 - Fields Flashcards

Gravitational fields, Electric fields, Capacitors, Magnetic fields, Electromagnetic induction.

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1
Q

What is a gravitational field?

A

The force field round a mass.

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2
Q

What is a field line (gravitational)?

A

The path a smaller mass would follow if pulled towards a larger mass.

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3
Q

Define the strength of a gravitational field (g)

A

The force per unit mass on a small test mass placed in the field.

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4
Q

Describe a radial field

A

The field lines are like the spokes of a wheel, towards the centre.

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5
Q

What happens to g in a radial field?

A

Decreases with increasing distance from the massive body.

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6
Q

Describe a uniform field

A

Field lines are parallel and equally spaced.

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7
Q

What happens to g in a uniform field?

A

Magnitude and direction of g is constant.

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8
Q

Define gravitational potential energy

A

The energy of an object due to its position in a gravitational field.

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9
Q

Define gravitational potential

A

Gravitational potential at a point is the work done per unit mass to move a small object from infinity to that point.

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10
Q

What are equipotentials?

A

Surfaces of constant potential.

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11
Q

Define potential gradient (gravitational)

A

Potential gradient at a point in a gravitational field is the change in potential per metre at that point.

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12
Q

What is Kepler’s Third Law?

A

For all planets r^3/T^2 is the same.

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13
Q

What are the assumptions in Newton’s law of gravitation?

A

Always attractive
Proportional to the mass of each object
Proportional to 1/r^2 (r is distance between objects)

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14
Q

What is the name for G?

A

Universal constant of gravitation

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15
Q

Define escape velocity

A

The minimum velocity an object must be given to escape from the planet when projected vertically from the surface.

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16
Q

What is the formula to remember for escape veloctiy?

A

v(esc)=sqrt(2gR)
g is gravitational field strength
R is the radius of the planet

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17
Q

What is the height of a geostationary satellite above the Earth?

A

35600km

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18
Q

What do electrical conductors contain a lot of?

A

Free electrons

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19
Q

What do electrically insulating materials not contain?

A

Free electrons

20
Q

What is a field line (electric)?

A

The path a free positive test charge follows.

21
Q

Describe a field between two oppositely charged plates

A

Field lines run parallel
At right angles to the plates
At the edges of the field the lines are slightly curved

22
Q

What kind of a field is it between two oppositely charged plates?

A

Uniform field

23
Q

Define electric field strength at a point in the field

A

The force per unit charge on a positive test charge placed at that point.

24
Q

Electric field strength between plates is proportional to what?

A

Q/A
Q - charge
A - surface area

25
Q

Define electric potential at a point in an electric field

A

Work done per unit positive charge on a positive test charge when it is moved from infinity to that point.

26
Q

Define potential gradient (electric) at a point in an electric field

A

The change of potential per unit change of distance in a given direction.

27
Q

How is potential gradient effected if the field is non-uniform?

A

Varies according to position and direction.

Closer equipotentials means greater potential gradient at right angles to them.

28
Q

How is potential gradient effected if the field is uniform?

A

Equipotentials between the plates are equally spaced parallel to the plates.
Potential gradient is constant.

29
Q

Define electric field strength

A

The negative of the potential gradient.

30
Q

In Coulomb’s law, force is proportional to what?

A

Proportional to the product of the charges

Inversely proportional to the square of the distance between them

31
Q

What is a point charge?

A

An expression for a charged object in a situation where distances under consideration are much greater than the size of the object.

32
Q

If two forces are in the same direction, what is the resultant electric field strength formula?

A

E(1) + E(2)

33
Q

If two forces are in opposing direction, what is the resultant electric field strength formula?

A

E(1) - E(2)

34
Q

If two forces are at right angles to each other, what is the resultant electric field strength formula?

A

sqrt(E(1)^2 + E(2) ^2)

35
Q

What is the constant of proportionality in electrostatic fields?

A

1/4πε(0)

36
Q

What is a capacitor?

A

A device designed to store charge.

37
Q

How does a capacitor work?

A

Two parallel metal plates placed near each other. When connected to a battery, electrons move through the battery and are forced onto one of the plates. On the other plate, an equal number of electrons leave that plate.

38
Q

What is the symbol for a capacitor in a circuit?

A

Two equal length parallel lines.

39
Q

How can a capacitor’s pd be measured when it is charging?

A

Use a stopwatch and measure the voltmeter at set times.

Use a data logger.

40
Q

What would a charge against pd graph for a capacitor look like?

A

A straight proportional line passing through the origin.

41
Q

Define capacitance

A

The charge stored per unit pd.

42
Q

How is the energy stored in a capacitor obtained from a graph?

A

Charge against pd graph

Area under is a triangle of QV/2

43
Q

In what proportionality does current, charge and pd of a capacitor decrease?

A

Exponentially

44
Q

What is the time constant of a circuit?

A

RC

45
Q

When t=RC in a capacitor’s discharge, what percentage charge remains?

A

37%

46
Q

When t=2RC in a capacitor’s discharge, what percentage charge remains?

A

14%

47
Q

At what point, is a capacitor considered discharged?

A

When t=5RC

RSFC Physics (13 decks)

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