Gravitational and Electric Fields

Question 1

Newton’s Law of Gravity

Answer 1

an attractive force between two point masses

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

Question 2

Concept of a force field

Answer 2

the region in which a body experiences a force

Question 3

Representation of gravitational field lines (radial and uniform fields)

Answer 3

field lines show direction of force on a point mass in a gravitational field.

Question 4

Equipotential

Answer 4

Line joining points of equal potential

No work is done moving an object along an equipotential

Question 5

Gravitational field strength, g

Answer 5

the force acting per unit mass

Question 6

Gravitational field strength units

Answer 6

N kg-1 VECTOR

Question 7

Gravitational potential, V, (at a point)

Answer 7

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

Question 8

Units of gravitational potential

Answer 8

J kg-1 SCALAR

Question 9

Gravitational potential, V, at infinity

Answer 9

zero

Question 10

Gravitational potential difference, V, between two points

Answer 10

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

Question 11

Area under graph of gravitational field strength against r

Answer 11

work done moving a unit mass between the two points

Question 12

Gradient of graph of gravitational potential against r

Answer 12

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

Question 13

Energy considerations of an orbiting satellite

Answer 13

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

Question 14

Features of a geosynchronous orbit

Answer 14

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

Question 15

Escape velocity of an object from a planet

Answer 15

loss of kinetic energy = gain in grav. potential energy

to get to infinity, need to provide grav. potential energy

Question 16

Coulomb’s Law

Answer 16

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.

Question 17

Representations of electric field lines

Answer 17

field lines show direction of force on a point positive charge in an electric field.

Question 18

Electric field strength, E

Answer 18

force acting per unit charge on a POSITIVE charge.

Question 19

Electric field strength units

Answer 19

N C-1 or V m-1 VECTOR

Question 20

Electric potential, V, (at a point)

Answer 20

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

Question 21

Units of electric potential, V

Answer 21

J C-1 or V (Volts) SCALAR

Question 22

Electric potential, V, at infinity

Answer 22

Zero

Question 23

Electric potential difference, V, between two points

Answer 23

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

Question 24

Path of charged particle in a uniform electric field

Answer 24

Path is PARABOLIC, because,

Magnitude of force is constant and always in the SAME direction

Question 25

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

Answer 25

Loss of electrical potential energy = gain in kinetic energy

QV = 1/2mv^2

Question 26

Similarities between electric and gravitational fields

Answer 26

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.)

Question 27

Differences between electric and gravitational fields

Answer 27

masses always attract but charges may attract or repel