Fields: gravitational and electric

Question 1

On a force diagram for gravity, and an object is moved away from an object producing a gravity field, how does the diagram show that the force felt has been reduced?

Answer 1

The no. of lines will be less further away, meaning less force.

Question 2

what is gravitational field strength?

Answer 2

the force per unit mass

Question 3

what does the area under a graph of g against r show?

Answer 3

gravitational potential ,V

Question 4

what is gravitational potential ?

Answer 4

the gravitational potential energy that a unit mass at that point would have.

Question 5

explain the gravitational field equation.

Answer 5

G is the gravitational constant. M is the mass of the object creating the gravity field and r is the radius of the object.

Question 6

what is the gravitational potential at infinity?

Answer 6

0. Other wise it is negative.

Question 7

how can a graph of gravitational potential against radius be used to find g?

Answer 7

Draw a tangent to the curve at a point. Then use g=Δv/Δr

Question 8

what is the shape of the orbits of the plants and the moon?

Answer 8

So close to a circle, we can assume them to be circular.

Question 9

When an object orbits around a planet, what does that mean for the centripetal and gravitational forces?

Answer 9

They are equal. Thus the equations can be made equal to each other and rearranged.

Question 10

how can the speed an object orbits a planet be calculated?

Answer 10

make the gravitational and centripetal force equations equal to each other. re arrange to give v=(GM/r)^0.5

Question 11

What is the equation used to find the time period of an orbit?

Answer 11

T=((4π²r³)/(GM))^0.5it is a product of the velocity of orbit equation and a circular motion one for the period.

Question 12

what does any object with a charge have around it?

Answer 12

An electric field.

Question 13

What are the units for electric charge?

Answer 13

Coulomb.

Question 14

What will a charged object in an electric field feel?

Answer 14

A force.

Question 15

If the force between 2 charges is negative, what will happen between the charges?

Answer 15

They feel an attractive force.

Question 16

what is electric field strength?

Answer 16

The force per unit positive charge. The force that a charge of +1C would feel in the electric field.It is a vector pointing in the direction a positive charge would go.

Question 17

How can a electric uniform field get produced ?

Answer 17

Connecting 2 parallel plates to opposite poles of a battery.

Question 18

How will a uniform electric field between 2 plates get draw?

Answer 18

Arrows will go from the positive to negative plate. Here will be lines perpendicular to the arrows, indicating pd. Each one of the lines will have the same pd across it and it will be the original pd at the positive plate and 0 at the negative one.

Question 19

What affects the size of electric potential?

Answer 19

The distance from the object creating the field and the strength of the charge of said object.

Question 20

explain the main features of a low earth orbit.

Answer 20

Orbital period is a few hours Earth rotates relative to the orbit Many orbits with different radii and periods are possible Orbit height is less than geosynchronous satellite Speed is greater than that of geosynchronous satellite Satellite scans the whole surface of the Earth Applications: surveillance of conditions/installations on Earth,mapping, weather observations, environmental monitoring Gives access to every point on Earth’s surface every day Can collect data from regions inaccessible to man Contact with transmitting/receiving aerial is intermittent Aerial is likely to need a tracking facility Lower signal strength required than that for geosynchronoussatellite

Question 21

explain the features of geosynchronous orbit.

Answer 21

Orbital period matches Earth’s rotational period exactly Satellite maintains same position relative to Earth Only one particular orbit radius is possible Travels west to east above Equator (in same direction as Earth’srotation) Orbit height is greater than polar orbit satellite Speed is less than that of polar orbiting satellite Scans a restricted (and fixed) area of the Earth’s surface only Applications: telecommunications generally, cable and satelliteTV, radio, digital information, etc. Satellite is in continuous contact with transmitting/receiving aerial Aerial can be in a fixed position Higher signal strength required than that for polar satellite

Question 22

what are some of the similarities between electric and gravitational fields?

Answer 22

both are force by unit something(charge or mass)they both have inverse square relationshipsfield lines for a point mass and negative point charge go the same way.potential is 0 at infinity

Question 23

what are some of the differences between electric and gravitational fields?

Answer 23

gravitational is always attractive while electric can be bothobjects can be shielded from electric fieldsthe size of a magnetic force depends on the medium it is going through.

Question 24

What is electric potential?

Answer 24

Electric potential is the work done per unit charge in bringing a small positive test charge from infinity to a point in an electric field.

Question 25

What is E and what are the units?

Answer 25

Electric field strength. Units newtons per coulomb.(NC⁻¹) or potential difference per metre. (Vm⁻)

Question 26

If the 2 ends of battery are connected to two parallel plates, what is the electric field strength?

Answer 26

It is the same for any point between the plates. Equal to potential difference of plates divided by distance.

Question 27

W=Q*V

What do the parts of this equation mean?

Answer 27

W= work done
Q= charge moved
V= change in potential

Question 28

What is electric potential for a positive charge?

Answer 28

It is positive. Negative for a negative charge.

Question 29

What is the volt equivalent to?

Answer 29

Joules per coulomb