Gravitational and Electric Fields (Unit 4) Flashcards Preview

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

Newton’s Law of Gravity

an attractive force between two point masses
proportional to the product of their masses and inversely proportional to their separation squared

2

Concept of a force field

the region in which a body experiences a force

3

Representation of gravitational field lines (radial and uniform fields)

See sheet

4

Equipotential

Line joining points of equal potential
No work is done moving an object along an equipotential

5

Gravitational field strength, g

the force acting per unit mass

6

Gravitational field strength units

N kg-1 VECTOR

7

Gravitational potential, V, (at a point)

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

8

Units of gravitational potential

J kg-1 SCALAR

9

Gravitational potential, V, at infinity

zero

10

Gravitational potential difference, V, between two points

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

11

Graphical variation of magnitude of g with r

See sheet

12

Graphical variation of V with r

See sheet

13

Area under graph of gravitational field strength against r

work done moving a unit mass between the two points

14

Gradient of graph of gravitational potential against r

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

15

Derivation of Kepler’s Law

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

Energy considerations of an orbiting satellite

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

17

Features of a geosynchronous orbit

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

Escape velocity of an object from a planet

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

Coulomb’s Law

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

Representations of electric field lines

See sheet

21

Electric field strength, E

force acting per unit charge on a positive charge.

22

Electric field strength units

N C-1 or V m-1 VECTOR

23

Electric potential, V, (at a point)

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

24

Units of electric potential, V

J C-1 or V (Volts) SCALAR

25

Electric potential, V, at infinity

Zero

26

Electric potential difference, V, between two points

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

27

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

See sheet

28

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

See sheet

29

Area under graph of electric field strength against r

See sheet

30

Path of charged particle in a uniform electric field

Path is parabolic, because,
Magnitude of force is constant and always in the same direction

31

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

Loss of electrical potential energy = gain in kinetic energy

QV = 1/2mv2

32

Similarities between electric and gravitational fields

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

Differences between electric and gravitational fields

masses always attract but charges may attract or repel
(see table on Pg 89 of A2 text book)