Gravitational and Electric Fields (Unit 4) Flashcards Preview

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Flashcards in Gravitational and Electric Fields (Unit 4) Deck (33)
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1
Q

Newton’s Law of Gravity

A

an attractive force between two point masses

proportional to the product of their masses and inversely proportional to their separation squared

2
Q

Concept of a force field

A

the region in which a body experiences a force

3
Q

Representation of gravitational field lines (radial and uniform fields)

A

See sheet

4
Q

Equipotential

A

Line joining points of equal potential

No work is done moving an object along an equipotential

5
Q

Gravitational field strength, g

A

the force acting per unit mass

6
Q

Gravitational field strength units

A

N kg-1 VECTOR

7
Q

Gravitational potential, V, (at a point)

A

work done per unit mass to move a small mass from infinity to that point.

8
Q

Units of gravitational potential

A

J kg-1 SCALAR

9
Q

Gravitational potential, V, at infinity

A

zero

10
Q

Gravitational potential difference, V, between two points

A

work done per unit mass to move a small mass from one point to the other.

11
Q

Graphical variation of magnitude of g with r

A

See sheet

12
Q

Graphical variation of V with r

A

See sheet

13
Q

Area under graph of gravitational field strength against r

A

work done moving a unit mass between the two points

14
Q

Gradient of graph of gravitational potential against r

A

gradient = -g (gravitational field strength); g= -(deltaV/delta r)

15
Q

Derivation of Kepler’s Law

A
  1. Gravitational force = centripetal force
  2. GMm/r2 = mv2/r or GMm/r2 = mr(omega)2
  3. substitute for v (v = (2pi x r)/T) or omega( omega = (2pi)/T)
  4. re-arrange to get T2 = ((4pi2)/GM) x r3
16
Q

Energy considerations of an orbiting satellite

A

Total satellite energy = kinetic energy + grav. potential energy
Total satellite energy = 1/2mv2 - GMm/r

17
Q

Features of a geosynchronous orbit

A
  1. orbits over equator
  2. maintains a fixed position relative to surface of Earth
  3. period is 24 hours (same as the Earth)
  4. offers uninterrupted communication between transmitter and receiver
  5. steerable dish is unnecessary
18
Q

Escape velocity of an object from a planet

A

loss of kinetic energy = gain in grav. potential energy
(to get to infinity, need to provide grav. potential energy)
= 1/2mv(escape)2 - GMm/r
gives v(escape) = Square root of 2GM/r

19
Q

Coulomb’s Law

A

magnitude of force between two point charges
is proportional to the product of their charge and inversely proportional to their separation squared
the force is ATTRACTIVE with un-like charges and REPULSIVE with like charges.

20
Q

Representations of electric field lines

A

See sheet

21
Q

Electric field strength, E

A

force acting per unit charge on a positive charge.

22
Q

Electric field strength units

A

N C-1 or V m-1 VECTOR

23
Q

Electric potential, V, (at a point)

A

work done to move a small unit positive charge from infinity to the point

24
Q

Units of electric potential, V

A

J C-1 or V (Volts) SCALAR

25
Q

Electric potential, V, at infinity

A

Zero

26
Q

Electric potential difference, V, between two points

A

work done to move a small unit positive charge from one point to the other.

27
Q

Graphical variations of E with r (radial and uniform fields)

A

See sheet

28
Q

Graphical variations of V with r (radial and uniform fields)

A

See sheet

29
Q

Area under graph of electric field strength against r

A

See sheet

30
Q

Path of charged particle in a uniform electric field

A

Path is parabolic, because,

Magnitude of force is constant and always in the same direction

31
Q

Speed of charged particle accelerated across a potential difference, V

A

Loss of electrical potential energy = gain in kinetic energy

QV = 1/2mv2

32
Q

Similarities between electric and gravitational fields

A

field strengths are both inversely proportional to separation squared
potentials are both inversely proportional to separation
(see table on Pg 89 of A2 text book.)

33
Q

Differences between electric and gravitational fields

A

masses always attract but charges may attract or repel

see table on Pg 89 of A2 text book