gravitational and electric fields

Question 1

what is a force field?

Answer 1

a region where a body experiences a non contact force

Question 2

how do force fields arise?

Answer 2

from interactions between objects or particles or between masses.
only objects with a large mass have gravitational fields that produce a significant effect.

Question 3

what will happen to the gravitational force if you double the distance between two masses?

Answer 3

1/4 of the original force due to being directly proportionate to 1/r squared

Question 4

why is the law of gravitation an inverse law?

Answer 4

because it is radial

Question 5

what is gravitational field strength?

Answer 5

the force per unit mass/ the acceleration due to gravity

Question 6

is gravitational field strength vector or scaler?

Answer 6

vector

Question 7

what does the area under a g-r curve be used to find?

Answer 7

the gravitational potential

Question 8

what happens to g as you move further away from the earth?

Answer 8

g decreases with the inverse square law.

Question 9

what is gravitational potential at a point in the field?

Answer 9

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

Question 10

what is an equipotential?

Answer 10

points with the same gravitational potential. no work is done by the field when and object moves along it.

Question 11

how would you investigate orbital speed and period of planets in our solar system and why?

Answer 11

using the equations of circular motion because the planets have almost circular orbits.

Question 12

for a satellite, what force keeps it in its path and what causes this force?

Answer 12

centripetal force caused by its gravitational attraction to the mass its orbiting.

Question 13

how to find the orbital speed of a satellite without knowing the magnitude of the force

Answer 13

make (mv^2)/r = (GMm)/r^2
then rearrange and cancel to find r

Question 14

what’s the relationship between the orbital speed and radius of a satellite?

Answer 14

the orbital speed of a satellite is inversely proportional to the square root of its orbital radius

Question 15

how to work out the orbital time period T?

Answer 15

time = distance/ speed
T= (2 x pi x radius) / v

Question 16

kinetic and potential energy in circular orbits

Answer 16

orbital speed and distance above the mass its orbiting are always constant this means KE and PE also remain constant.

Question 17

kinetic and potential energy in a elliptical orbit

Answer 17

satellite will speed up as its orbital radius decreases so KE will increase and PE will decrease. (opposite aswell) total energy remains constant.

Question 18

what is escape velocity?

Answer 18

the minimum speed an unpowered object needs in order to leave the gravitational field of a planet and not fall back to the planet due to the gravitational attraction.

Question 19

how to derive equation for escape velocity

Answer 19

kinetic energy lost= gpe gained
(1/2) mv^2 = GMm/r
rearrange and cancel for v
r is the radial distance from the centre of the planet to the object

Question 20

what’s a synchronous orbit? give an example of one

Answer 20

when an orbiting object has an orbital period equal to the rotational period of the object its orbiting.
for example, geostationary satellites always directly above the equator. travel at the same angular speed as the earth turns and same direction.

Question 21

how low is a low orbiting satellite?

Answer 21

between 180 and 2000km above earth

Question 22

advantages of low orbiting satellites

Answer 22

cheaper to launch
require less powerful transmitters
useful for communications
high level of detail of earth surface

Question 23

disadvantage of low orbiting satellites

Answer 23

you need multiple satellites working together to get full coverage due to the high orbital speed of the satellite compared to earth.

Question 24

what’s Coulomb’s law?

Answer 24

a way you can calculate the force on a charged object in an electric field. it gives the force of attraction or repulsion between two point charges (always equal and opposite) in a vacuum.
another case of the inverse square law

Question 25

if the point charges aren’t in a vacuum then what effects the size of the force

Answer 25

the permittivity of the material between them (air can be treated as a vacuum)

Question 26

what’s electrical field strength?

Answer 26

the force per unit charge.
its a vector that points in the direction that a positive charge would move
dependant or where you are in the field

Question 27

how can an electrolytic tank be used to measure field lines?

Answer 27

you have a tank of water with positive and negative ions dissolved in it
electrodes are put into the water to create a positive change one end and negative the other
a voltmeter is then used to find points within the water where pd is the same so we can map out equipotentials and field lines

Question 28

what is absolute electric potential at a point?

Answer 28

the electrical potential energy that a unit positive charge would have at that point. dependant on how far it is from the charge creating the field and the size of the charge

Question 29

where is electric potential greatest?

Answer 29

on the surface of the charge

Question 30

what happens to electric potential and the distance from the charge increases?

Answer 30

it will decrease
V will be 0 at an infinite distance

Question 31

what does the gradient of a V-r graph give (V=electric potential)?

Answer 31

the field strength at that point

Question 32

what is the electrical potential difference between two points?

Answer 32

the energy needed to move a unit charge between those points

Question 33

how can you find the electrical potential difference from a graph?

Answer 33

find the area under a electric field strength- r graph between the two points

Question 34

how can you derive the formula W=QV

Answer 34

E= V/d = F/Q
QV=Fd
W=Fd so W=QV

Question 35

state some similarities between gravitational and electric fields

Answer 35

g is force per unit mass
E is force per unit charge
newtons law of gravitation and coulombs law for electric charge between two points both have an inverse square law to r
field lines
both gravitation and electric potential per unit mass/charge and is zero to infinity
equipotentials

Question 36

difference between gravitational and electric fields

Answer 36

gravitational always attractive whereas electrostatic can be repulsive

Question 37

what happens to gravitational and electric fields at subatomic levels?

Answer 37

the distances between the particles become tiny but because they have very small mass the gravitational force is much weaker then the electrostatic force

Question 38

State what is represented by gravitational field lines.

Answer 38

Gravitational field lines show the direction (and relative magnitude) of
force on a mass (placed in the force field)