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

QV = 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.)

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