u4: fields

Question 1

field

Answer 1

region in space around an object where object exerts force on another

Question 2

examples of forces tht have fields associated w/ them

Answer 2

• gravitational
• magnetic
• electric

Question 3

newtons law of universal gravitation

Answer 3

FG=Gm1m2/r^2

• FG: grav attr’n btwn two objs (N)
• G: 6.67 x 10^-11
• m1m2: masses of both objects (kg)
• r: centre-to-centre distance

Question 4

you have three asteroids arranged in a line. you need to find the net gravitational force acting on one of them. how do u do this?

Answer 4

1. draw FBD for forces acting on needed asteriod
2. make directional compass
3. write F(C) = F(AonC) (+/-) F(BonC)
4. put direction in answer

Question 5

gravitational field strength? when is it used?

Answer 5

• used when finding force of gravity of objects on a planet

g= Gm / r^2
- m: mass of planet
- r: radius of planet

Question 6

relationship btwn field strength and distance from a planet’s centre?

Answer 6

inverse square relationship: as distance from planet centre increases, gravitational field strength decreases rapidly

Question 7

how do u solve satellite questions?

Answer 7

1. draw a diagram. find the distance btwn centre of planet and satellite w/ wtvr info u have
2. plug into g=Gm/r^2 where m is mass of satellite
3. if asked for gravitational force of any object at that point: do Fg=mg where g is the value u just calculated in S2

Question 8

what keeps moon/satellites in orbit around earth?

Answer 8

gravity

Question 9

what shape is orbits

Answer 9

circular

Question 10

what kind of motion do satellites and moon undergo

Answer 10

centripetal motion

Question 11

how do you find the net centripetal force acting on an orbiting object?

Answer 11

F(c) = ma(c) = mv^2 / r

Question 12

formulas for orbital speed

Answer 12

v^2 = GM/r
- v is speed in m/s
- M os mass of central body
- r is orbital radius (centre to centre)

v = 2πr/T
- T is orbital period

Question 13

relationship btwn orbital speed and distance from planet

Answer 13

orbital speeds decrease as u move further from the sun

Question 14

what is orbital period

Answer 14

T
- time for orbiting object to complete a rotation

Question 15

geosynchronous orbits

Answer 15

• geosyn. satellites orbit at same speed as earth turns
• orbital period is 24 hours
• if located above earth’s equator, they stay in a fixed spot and are called geostationary
• used for weather and terrestrial monitoring

Question 16

electric field strength formula is E=kQ/r^2
units?

Answer 16

• E: electric field strength, N/C
• Q: charge, C
• r: distance btwn masses
• k: coulombs constant

Question 17

wht is electric field similar to?

Answer 17

gravitational field

Question 18

wht does density of field lines show?

Answer 18

strength of electric field

Question 19

do electric field lines ever cross?

Answer 19

no

Question 20

what’s the direction of electric field lines?

Answer 20

• start at positive, end at negative
• out of +
• into -

Question 21

are field lines curved or jagged?

Answer 21

curved

Question 22

relationship btwn electric field and plate charge/unit area, q, in parallel plates

Answer 22

E is proportional to q
- unless plates attached to battery

Question 23

how would moving parallel plates further apart impact the electric field intensity?

Answer 23

• does nothing
• only plate charge/unit area impacts intensity

Question 24

how to find electric force when given a known field?

Answer 24

F = qE
- if q is negative, it acts in opposite direction. so plug in -‘ves here!

Question 25

nC to C

Answer 25

divide by 10^9

Question 26

µC to C

Answer 26

divide by 10^6

Question 27

work when forces are repulsive vs attractive

Answer 27

- both positive: work brings charges together - opposite charge: work pulls charges apart

Question 28

how is work stored between q1 and q2?

Answer 28

as electrical potential energy

Question 29

what is work equal to?

Answer 29

- change in electric potential energy - W=Kq1q2/r = EE - include charge signs here

Question 30

units of work

Answer 30

J

Question 31

what is voltage?

Answer 31

Q - electric potential due to a single point - potential energy per unit positive charge at any point in space due to single point charge Q

Question 32

formula to find potential bc of voltage at r? what kind of quantity is this? relationship in it?

Answer 32

V=KQ/r - scalar quantity - if Q>0, V>0 - if Q<0, V<0

Question 33

equipotential surfaces

Answer 33

- every surface has same surface potential - electrical potential constant at given radius from Q - creates spherical surfaces where potential is constant - no work is done to move charges around on equipotential surfaces

Question 34

how do u find the total potential at a point where several charges are there?

Answer 34

V(t) = V1 + V2 + V3... - scalar - account for signs

Question 35

electron/proton symbol

Answer 35

e- and e+

Question 36

charge on electron/protons

Answer 36

e = 1.602 x 10^-19

Question 37

formula for finding charge on object based on number of changes gained/lost

Answer 37

q = ne - e: charge - n: number of them

Question 38

when electrons experience uniform force in uniform electric fields, wht happens

Answer 38

uniform acceleration

Question 39

what can uniform electric fields be used for?

Answer 39

- change speed of charged particle - deflect particle

Question 40

charge of electrons/protons

Answer 40

1.6 x 10^-19