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Henry Physics RSFC > Equations Paper 2 Explained > Flashcards

Equations Paper 2 Explained Flashcards

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1
Q

What is the equation for orbital velocity of an object orbiting in a gravitational field (satelite orbiting a planet)?

A

Vorb = (GM/r)1/2

G - gravitational constant (Nm2kg-2)
M - mass of object creating the field (kg)
r - radius of the orbit from the centre of M (m)

This isn’t on the formula sheet

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2
Q

What is the equation for potential energy at a point in gravitational fields?

A

Ep = GMm/r = v * m

Ep - gravitational potential energy (J)
G - gravitational constant (Nm2kg-2)
M - mass of the object creating the field (kg)
m - mass of the object in the field (kg)
v - gravitational potential at that point in the field (J/kg)

This isn’t on the formula sheet

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3
Q

What is the equation for gravitational field strength below the surface of the object creating the field (inside a planet)?

A

g = 4/3 πpGR

g - gravitational field strength (N/kg)
p - density (kgm-3)
G - gravitational constant (Nm2kg-2)
R - distance from centre of sphere to the object (m)

This isn’t on the formula sheet

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4
Q

What is the equation for escape velocity of an object thats in a gravitational field (ball on a planet)?

A

Vesc = (2GM/r)1/2

G - gravitational constant (Nm2kg-2)
M - mass of object creating the field (kg)
r - distance from the centre of mass of M to where the object is starting from (m)

This isn’t on the formula sheet

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5
Q

What formula is used for a substance which changes temperature, in order to find the energy change and what do the symbols mean?

A

Q = mc θ
Q - the energy input (heat) needed in J
m - mass of the substance in kg
c - specific heat capacity J kg-1 K-1
θ - change in temperature in K

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6
Q

What is the formula for a substance changing state and the energy released and what do the symbols mean?

A

Q = ml
Q - the energy input needed to change state in J
m - mass of the substance in kg
l - specific latent heat of fusion or vaporisation in J Kg-1

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7
Q

What is the equation relating the time of an orbit and the radius of an orbit?

A

GMT2=4π2r3

G - gravitational constant (Nm2kg-2)
M - mass of the object creating the field (kg)
T - time period of orbit (s)
r - radius of the orbit from the centre of mass of M (m)

This isn’t on the formula sheet

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8
Q

How is the work done on an object found in gravitational fields and what are the symbols for the equation used?

A

ΔW = mΔV

W - work done on the object (J)
m - mass of the object which is having work done on it
V - change in potential of the object

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9
Q

What is the equation for electric potential energy in electric fields?

A

Ep = 1/4πε0 * Qq/r = v * q

Ep - electric potential energy (J)
ε0 - permittivity of free space (Fm-1)
Q - charge of the charge creating the field (C)
q - charge of the charge in the field (C)
r - distance q is from Q (m)
v - electric potential at that point (JC-1)

The second one isn’t on the formula sheet

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10
Q

What formula is used for a charge moving in a uniform electric field?

A

F = EQ

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11
Q

What is the formula for gravitational potential and what does this give us?

A

V = GM/r
This gives gravitational potential at a point

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12
Q

What are the capacitor charging equations?

A

Q = Q0(1-e-t/RC) Q0 = final charge

V = V0(1-e-t/RC) V0 = final voltage

I = I0(1-e-t/RC) I0 = inital current

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13
Q

What are the capacitor discharging equations?

A

Q = Q0e-t/RC Q0 = initial charge

V = V0e-t/RC V0 = initial voltage

I = I0e-t/RC I0 = initial charge

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14
Q

What are the formulas for gravitational field strength at a point?

A

g = GM/r2
g = F / m

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15
Q

What is the equation for the radius of the path of a charged particle moving in a magnetic field?

A

r = mv/BQ

r - radius of circular path (m)
m - mass of particle (kg)
B - magnetic flux density (T)
Q - charge of the moving particle (C)
v - linear velocity of the moving particle (ms-1)

This isn’t on the formula sheet

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16
Q

What is the equation for the velocity that will be selected in a mass spectrometer (where magnetic force = electric force)?

A

v = E/B

v - velocity of particle that will be selected (ms-1)
E - electric field strength (NC-1)
B - magnetic flux density (T)

This isn’t on the formula sheet

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17
Q

What is the formula for electric potential and what must you know when using it

A

V = 1/4πε0 Q/r
This is electric potential at a point

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18
Q

What is the standard formula for capacitance and what do the symbols mean?

A

C = Q/V
From the definition of capacitance which is the charge stored per unit voltage
Q - charge across the capacitor (C)
V - potential difference across the capacitor (V)
C - capacitance of the capacitor (F)

19
Q

What is the more edgy formula for capacitance and what do the symbols mean?

A

C = Aε0εr / d
C - Capacitance of capacitor (F)
A - Cross-sectional area of the plates overlap (m2)
ε0 - permittivity of free space (F/m)
εr - relative permittivity (no units)
d - distance between the plates (m)

20
Q

What are the formulas for energy stored by a capacitor?

A

E = 1/2 * QV = 1/2 * CV2 = 1/2 * Q2 / C
All values represent that of which is across the capacitor

21
Q

What is the time constant formula?

A

T = RC
T - time taken for charge to fall to 37% of its original value
R - Resistance in the circuit
C - Capacitance of the capacitor

22
Q

How is the force on a current due to a magnetic field found?

A

F = BIL (sinθ)
Use sinθ to get perpendicular length to the field

23
Q

How is the force on a moving charge in a magnetic field calculated?

A

F = BQv
when v is the velocity of the charge

24
Q

What is the formula for the torque of a coil rotating in a DC motor?

A

Torque (Nm) = BILNd

N - number of coils
d - distance between coplanar forces
L - length of coil

This isn’t on the formula sheet

25
Q

How do you calculate magnetic flux?

A

Φ = BA

Φ - magnetic flux (Wb)
B - magnetic flux density which should be resolved perpendicular to the area
A - Area which flux is passing through

26
Q

How do you calculate flux linkage?

A

Using Φ = BA —> NΦ = NBA
NΦ - Flux linkage (Wb turns)
B must be perpendicular flux density to the coils

27
Q

What is the standard formula for the magnitude of an induced emf?

A

ε = N * ΔΦ/Δt

ε - induced emf (V)
Other side of formula is change in flux linkage

28
Q

What is the formula for flux linkage in a rotating coil?

A

NΦ = BAN cos (wt) OR cos (θ)

29
Q

What is the formula for the magnitude of an induced emf in a rotating coil?

A

ε = BAN ω sin ωt

t- time the coil has been turning for

This is the negative derivative of the flux linkage formula as emf is the negative gradient

30
Q

What is the formula for Irms and what does this actually mean?

A

Irms = I0 / root 2

Irms is the DC supply which would provide the same average power per cycle as the AC supply

31
Q

What is the formula for Vrms and what does this actually mean?

A

Vrms = V0 / root 2

Vrms is the DC supply which would provide the same average power per cycle as the AC supply

32
Q

What is the standard transformer equation and can it only be used in certain situations?

A

N/N2 = V/V2
Can be used regardless of efficiency

33
Q

How should you fill in values for the efficiency of transformers equation?

A

For the efficiency equation, write efficiency as a decimal if this is known and if not, then when solving for the efficiency note that the answer will be in decimal form

34
Q

What do Vp and Vs represent in transformer equations?

A

Vp - Voltage in the primary coil

Vs - Voltage in the secondary coil

35
Q

Can the formula N = N0e-λt be written in any other way?

A

Yes, can use A (activity) or C(Count rate) instead of N
(A = A0e-λt)
(C = C0e-λt)
λ - decay constant
t - time since initial decay

36
Q

What is the bog standard activity formula and what does it mean?
How else can activity be expressed?

A

A = λN
Activity is the number of unstable nuclei (N) multiplied by the decay constant
Activity can also be denoted by ΔN/Δt

37
Q

What is the formula for the radius of a nucleus and what do the symbols man!

A

R = R0A1/3
R - Radius of nucleus
A - Activity (Bq)
R0 - Radius of a hydrogen nucleus

38
Q

What formula links gravitational field strength and the force due to gravity and what does the mass in the equation represent?

A

g = F / m

m is the mass of the object which is worked upon by the field
(gravitational field strength is independent of the mass of the object in the field)

39
Q

How is the work done on an object found in electric fields and what do the symbols mean?

A

ΔW = QΔV

W - Work done on the object by the field (J)
Q - Charge thats in the field (C)
V - Change in potential (J/C)

40
Q

What is the formula for the electric field strength in a radial field and what must you know when using it?

A

E = 1/4πε0 Q/r2

This is the field strength at a point

41
Q

What does g = Δv / Δr tell you?

A

Field strength over short distances

42
Q

For w = qv and w = mv, what do q and m mean?

A

q and m are the charges/masses that are acted on by the field

43
Q

What is the equation for work done compressing a gas?

A

W = PΔV

W - Work done compressing or decompressing

P - Pressure that the gas is constantly at

ΔV - Change in volume of the gas

Henry Physics RSFC (27 decks)

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