A2 Physics 2021 Flashcards
Angular displacement in circular motion formula
arc length/radius
Radian definition
The angle subtended at the centre of a circle by an arc of length equal to the radius of the circle.
Speed in circular motion formula
v = (2πr)/t
Angular velocity in circular motion formula
w = θ/t = (2π)/t
Acceleration in circular motion is always towards the ______ of the circle
centre
Centripetal acceleration formula
a=v^2/r
Centripetal force formula
F=mv^2/r or F=mw^2r
A vehicle will not skid on a curved road if _______
Fcentripetal < Ffriction
What is an oscillation
The motion in which an object repeats the same movement in a regular cycle.
Angular frequency of an oscillation formula
w=2πf
Amplitude definition
Maximum displacement from equilibrium position.
Free oscillation definition
An object or system oscillating at it’s natural frequency with no external force applied other than the impulse that initiated the motion.
What is a restoring force
A force acting to push the object back to equilibrium position. Frestoring ∝ displacement
Acceleration in Simple harmonic motion formula
a=w^2r
What is a forced oscillation
When an oscillating object or system is driven by a periodic external force.
What is phase difference
The angle at which waves are out of phase - measured in radians
What is the derivative of sin
cos
What is the derivative of cos
-sin
Formula for speed at any point in an oscillation
v=w√x0 -x^2
Where x0 = amplitude
and x = displacement
Kinetic energy in SHM formula
Ek=1/2m^2A^2
Where A = amplitude
Maximum potential energy in a spring oscillation formula
Ep=1/2KA^2
Where A= amplitude
What is damping
A reduction in the amplitude of an oscillation as a result of energy lost from a system to overcome resistive forces acting in the opposite direction.
What is critical damping
When a system returns to equilibrium in the shortest possible time without crossing it due to a large damping force
What is light damping
When the resistive forces are light so the system passes through the equilibrium while decreasing amplitude.
What is heavy damping
When resistive forces are large. System returns to equilibrium slowly without crossing it.
What is natural frequency
When an oscillating system starts oscillating on its own at a frequency.
What is a driving/forced frequency
When a system oscillates from an external excitation with a frequency.
Resonance definition
An increase in amplitude that occurs when an oscillating system is forced to oscillate at it’s own natural frequency.
Occurs when Fnatural=Fdriving
What are some uses of resonance
Radio recievers, guitars
Sound intensity definition
The power delivered per unit area of a surface that is perpendicular to the direction of travel of the wave.
Intensity of a sound formula
I=Power/Area
NB: I∝1/r^2
How is ultrasound used in medical imaging
A high frequency (for high res) pulse is sent into the body and the echo is read as electrical signals to measure distance travelled.
What are 4 things that can be done to ultrasound waves
They can be: Reflected Refracted Scattered Absorbed
Acoustic energy definition
The disturbance of energy which passes through matter in the form of a wave
Acoustic impedance definition
A physical property which describes how much resistance an ultrasound pulse encounters as it passes through tissue
What is attenuation
The reduction of amplitude of a signal, electric current, or other oscillation.
What is a transducer
A device which produces ultrasound pulses- converts energy from 1 form to another.
What is a piezoelectric transducer
Introduces the ability to transmit high frequency ultrasound waves. Comprised of crystals such as quartz.
Acoustic impedance formula
Z = ρv
Transmitted intensity of ultrasound pulse equation
I = I₀ x e^-μx
Conservation of ultrasound intensity formula
I = Ir + It
Intensity reflection coefficient formula
α = (Z2-Z1)^2/(Z2+Z1)^2
How are ultrasound waves turned into images?
- Reflected waves return to transducer, transformed into voltage pulses.
- Voltage pulses amplified and processed to give image s.
What is an A-Scan
Amplitude scan - single transducer used to measure tissue depths
What is a B-Scan
Brightness scan - uses an array of transducers, each measuring amplitudes at a different angle, and plots each returning signal as a pixel on screen.
What are fixed points
Reference points on a thermometer - determined by physical properties of common materials.
What is absolute zero
The point of minimum motion of particles making up a substance.
What is triple point
The temperature at which all three phases of a substance exist.
What can be deduced from the difference in temp of 2 objects?
The rate of transfer of thermal energy
What is the basic principle by which temperature is measured
By measuring physical changes in the thermometric properties of a substance.
Why will some thermometers not give the same temperature reading for substance
For some thermometers, change in temperature may not be linear with change in thermometric properties.
What are the advantages of a thermocouple over a thermistor
- wider temp range
- linear scale
What are the advantages of a thermistor over a thermocouple
- smaller
- doesn’t require reference liquid.
- can be used remotely more easily
What is the ideal gas equation
PV = nRT
What are the 5 assumptions of the kinetic theory of ideal gas.
- Collisions of particles are completely elastic
- There are no external forces between molecukes
- Molecules move with constant velocity
- Total volume of molecules is much less than total volume of the gas
- Motion of the molecules is completely random
Heat definition
Total energy of all molecular motion inside an object
Temperature definition
Average kinetic energy of particles within a substance.
Specific heat capacity formula
Q=mcΔt
Specific latent heat formula
Q=mL
Why is latent heat of vaporization higher than latent heat of fusion?
Energy required to completely separate molecules is much greater than slightly seperate them.
What is internal energy
The sum of all Ek and Ep in a system.
What is the first law of thermodynamics
The total energy in an isolated system is constant
Internal energy formula
ΔU = Q + W
Work done on a contained gas formula
W = PΔV
What are the 2 types of capacitor
- Isolated
- Parallel plates
Capacitance definition
The ability of an electric system to collect and store energy in the form of electrical charge.
Capacitance formula
c = Q/V
Capacitance unit
Farad, F
Energy store in electric field formula
E=1/2QxV (are under graph)
Capacitance of air filled capacitor formula
c=ε₀x(A/D)
Capacitance of dielectric filled capacitor formula
c=ε₀εᵣx(A/D)
How will a potential difference be applied between plates of a capacitor
- Electrons at plate A will have more electrical potential energy causing electrons to move to plate B.
- This will cause a deficit of electrons at plate A and a surplus of electrons at plate B.
- This creates an electric field between the two plates in the direction of positive to negative. (E=V/D)
Work done between parallel plates formula
W=QV
Electrical potential energy formula
Ep=QV
What is the net charge in the centre of a capacitor
Zero
How is energy stored in a capacitor
In an electric field in the form of charges
2 uses of capacitors
- Storing energy
- Blocking D.C. in circuits
Charging a capacitor formula
Q=It
Time taken to charge a capacitor formula
T=RC
R=Resistance
C=Capacitance
3 applications of op-amp
- Acting as a switch when voltage reaches certain level
- Amplifying voltage and current signals
- Voltage comparator
Formula for Vout of op-amp
Vout = A₀(V+ - V-)