Physics (Rules & formulae) R#3 Flashcards
What is the formula for density?
Density = mass x volume
What is the formula for speed?
Speed = distance / time
What is the formula for weight?
Weight = mass x gravity
What is the formula for acceleration?
Acceleration = (final velocity – initial velocity) / time
What are the two formulas for pressure?
- Pressure (in solids) = Force / Area
- Pressure (in liquids) = Rho (density) x gravity x depth
What is the formula that links force, mass, and acceleration?
Force = mass x acceleration
What is the formula for moment?
Moment = Force x perpendicular distance from pivot
What is the formula for spring constant (K)?
Spring constant (K) = Force / Extension
What is the formula for work?
Work = Force x distance
What is the formula for gravitational potential energy (GPE)?
GPE = mass x gravity x height
What is the formula for kinetic energy (KE)?
KE = (½ mass) x velocity²
What are the 4 formulas given for power? (mechanical)
- Power = Work / time
- Power = Energy / time
- Power = (Force x distance) / time
- Power = Force x Velocity
What is the formula for momentum?
Momentum = mass x Velocity
How is change in momentum expressed when the directions are the same?
Change in momentum = mass x (final – initial velocity)
How is change in momentum expressed when the directions are different?
Change in momentum = mass x (final + initial velocity)
What is the impulse formula (with notation)?
Impulse = Force x time
(I = ΔP)
What is another way to express change in momentum?
Change in momentum = Force x time
What is the formula for energy in terms of heat?
Energy = mass x specific heat capacity x change in temperature
(Unit note: Q unit: J, c unit: J/kg°C)
How is wavelength defined?
Wavelength = Total distance / Number of waves
How is frequency calculated?
Frequency = Number of waves / Total time
(Unit: Hz)
How is frequency related to wave speed and wavelength?
Frequency = Wave speed / Wavelength
(Unit: Hz)
What are the two formulas for periodic time?
- Periodic Time = 1 / Frequency
- Periodic Time = Total time / Number of waves
How is wave speed determined?
Wave speed = Wavelength / Periodic time
What is the formula for the speed of sound in an echo?
Speed of sound in echo = 2 x distance travelled / Total time
(d > 17m)
What is the refractive index for light going from a lower density medium (air) to a higher density medium?
Refractive index = Sine of angle of incidence / Sine of angle of reflection
(Unitless | Air to Medium)
What is the refractive index for light going from a higher density medium to a lower density medium (air)?
Refractive index = Sine of angle of reflection / Sine of angle of incidence
(Unitless | Medium to Air)
How is the sine of the critical angle expressed?
Sine of critical angle = 1 / Refractive index of medium
Higher density medium to a lower density medium (air)
How can refractive index be expressed using the speed of light?
Refractive index = Speed of light in air / Speed of light in medium
(Unitless)
What is the formula for current?
Current = Charge / time
(Q unit: Coulomb (C) / I unit: Amperes (A))
What are the formulas for voltage?
- Voltage = Work / Charge
- Voltage = Energy / Charge
(Q unit: Coulomb (C) / V unit: Volts (V))
How do you calculate the gradient of a line?
Gradient = (y₂ – y₁) / (x₂ – x₁)
How is acceleration determined from a speed-time graph?
Acceleration = slope/gradient of the speed-time graph
How is the total distance in a speed-time graph found?
Total distance = area under the graph
How is total pressure at a point inside a liquid calculated?
Total pressure = atmospheric pressure + pressure due to liquid
What are the two conditions for equilibrium, rest, or balance?
- No resultant force acts on the object: Force (Up) = Force (Down) and Force (Right) = Force (Left)
- No resultant turning effect: Total moment clockwise = total moment anticlockwise
How is extension defined?
Extension = Final length – Original length
How are gravitational potential energy (GPE) and kinetic energy (KE) related when there is no air resistance?
GPE at max height = KE just before touching ground
What does the law of conservation of energy state?
Energy cannot be created nor destroyed, only transferred from one form to another OR Total energy = constant
How is resistance calculated according to Ohm’s law?
Resistance = Voltage / Current
(R unit: Ohms (Ω))
How is resistance calculated using the resistivity constant?
Resistance = (Rho [resistivity constant] x length of wire) / Cross-sectional area of wire
(R unit: Ohms (Ω) / L & A unit: m)
What is the formula for electrical energy?
Electrical energy = Current x Voltage x time
What are the 3 formulas for power in an electrical circuit?
- Power = Current x Voltage
- Power = Current² x Resistance
- Power = Voltage² x Resistance
How are GPE and KE related when there is air resistance and initial energy?
GPE at max height + Initial energy = KE before touching ground + Energy lost
How is efficiency calculated using work done and input energy?
Efficiency (%) = (work done / input energy) x 100
How is efficiency calculated using useful output energy?
Efficiency (%) = (useful output energy / input energy) x 100
How is efficiency calculated using useful output power?
Efficiency (%) = (useful output power / input power) x 100
What does the law of conservation of momentum state?
Total momentum before collision = total momentum after collision
What is the formula for an elastic collision and its key property?
- m₁u₁ + m₂u₂ = m₁v₁ + m₂u₂
- There is no energy lost
What is the formula for a perfect inelastic collision and what are the two key properties?
- m₁u₁ + m₂u₂ = V(m₁ + m₂)
- There is energy lost due to collision
- The colliding objects join together
What is Boyle’s Law at constant temperature?
P₁V₁ = P₂V₂
What is the law regarding the angle of incidence and reflection?
Angle of Incidence = Angle of refelection
Under what condition will a wave diffract when passing through a gap?
If the wavelength of a wave passing through a gap is greater than the gap then it will diffract
For water wavefronts, what happens when a wave goes from deep to shallow water? (3 points)
- It bends towards the normal
- Wavelength and speed decrease
- Frequency remains the same
For water wavefronts, what happens when a wave goes from shallow to deep water? (3 points)
- It bends away from the norma
- Wavelength and speed increase
- Frequency remains the same
For light waves, what happens when light goes from air to a medium? (3 points)
- It bends towards the normal
- Wavelength and speed decrease
- Frequency remains the same
For light waves, what happens when light goes from a medium to air? (3 points)
- It bends away from the normal
- Wavelength and speed increase
- Frequency remains the same
In a mirrored object, what is the relationship between object and image distances?
Distance between object and mirror = distance between mirror and image
Used to draw mirrored objects quickly in exam
For wires made of the same material with given diameters, how is the ratio of resistances calculated?
R₁/R₂ = (l₁/l₂) × (d₂²/d₁²)
For wires made of the same material with given cross-sectional areas, how is the ratio of resistances calculated?
R₁/R₂ = (l₁/l₂) × (A₂/A₁)
How do you get the direction of the magnetic field from a wire?
Use the right hand rule for a wire:
* Thumb: direction of current
* Curl: shows the magnetic field
How do you get the direction of the magnetic field from a coil?
Use the right hand rule for a coil:
* Thumb: direction of N-pole
* Curl: shows the direction of current
How do you determine the direction of magnetic force (motion) of a wire?
Use Fleming’s left hand rule:
* Thumb: direction of magnetic force (motion)
* Index finger: direction of the magnetic field from the magnet (north → south)
* Second finger: direction of current
How do you determine the direction of induced current in a wire?
Use Fleming’s right hand rule:
* Thumb: direction of motion
* Index finger: direction of the magnetic field from the magnet (north → south)
* Second finger: direction of induced current
