Definitions Flashcards
Gravitational potential at a point
The work done in bring a unit mass from infinity to a certain point.
Forced Frequency
The frequency of externally applied force
Importance of Faraday mesh
Faraday mesh is important to prevent external radio sources from interfering with the RF receiver
Purpose of large constant magnetic field
Causes nuclei to precess and align in the direction of the magnetic field and precess about the magnetic field. The precession is in the RF range
Purpose of non-uniform field
Since the Larmor Frequency depends on the magnetic field strength the Larmor frequency will be different in that specific region. Hence when RF of a specific frequency excites a specific slice the position of the nuclei can be determined.
Potential Divider Formula
Vout=R2/R1+R2 x E
Negative Feedback
Gclosed= Vout/Vin= Go/1+Go
Inverting Amplifier Gain
Gclosed= Vout/Vin= -Rf/Rin
Non- inverting Amplifier Gain
Gclosed= Vout/Vin= 1 + R1/R2
Op-Amp Gain
Gopen=Vout/(V+ - V-)
Gravitational Field Strength
g= GM/r^2
Orbital Period Geostationary Orbit
T^2= (4π^2/GM) x r^3
Kinetic Energy and Gas Formulas
Ek=1/2m
Ek=3/2kT
Ideal Gas Formulas
pV=nRT
pV=Nkt
pV=1/3Nm
p=1/3ρ
Electric Field Strength
E=Q/(4π x Eo x r^2)
Electrical Potential
V= Q/(4π x Eo x r)
Gravitational Potential
Φ = -GM/r
Formula for Kinetic Energy in SHM
Ekmax=1/2mw^2x^2
Ek=1/2mw^2(A^2-x^2)
Centripetal Acceleration 2 formulas
a=v^2/r
a=rw^2
Capacitance
The charge stored on one plate per unit of potential difference between the plates
What is negative feedback
When a fraction of output is combined with input. The output fraction is subtracted from the input. It reduces distortion due to increased bandwidth.
Magnetic Flux Density
B=Phi/A
Internal Energy
The sum of the random distribution of the kinetic and potential energies of the atoms or molecules in a system
Specific Heat Capacity
The energy required per unit mass of the substance to raise the temperature by 1K without a change in state
Coulomb’s Law
Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them.
Electrical Potential Definition
The electrical potential at a point is equal to the work done in bringing a unit positive charge from infinity to that point.
Newton’s Law of Gravitation
Any two point masses attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation.
Radian
The angle subtended at the center of a circle by an arc of length equal to the radius of the circle.
Root Mean Square velocity
The square root of the mean square speeds of all the particles’ velocities.
Speed in Circular motion
v=wr
Maximum Acceleration of SHM
a=-w^2x
Ratio of reflected intensity to the original intensity
Ir/Io = (Z2-Z1)^2 / (Z2+Z1)^2
Maximum velocity of SHM
v=Aw
Hall Voltage
V=BI/ntq
t is the thickness of the plate. d is the distance in the electric field, t is the thickness measured on the same side
Capacitors in series
1/Ctotal=1/C1 + 1/C2
The pd over them is divided so the charge must be the same on each plate.
Capacitors in parallel
Ctotal=C1 + C2
The pd over them is the same so the charge stored is different
Simple Harmonic Motion
When the acceleration is directly proportional to the opposite of the displacement. The direction is taken in reference to the equilibrium position
de Broglie Wavelength
lambda=h/p
Attenuation Constant
μ=ln2/x1/2
What is meant by gravitational force
The force acting between two masses
Arc length
Arc length = Angular distance x radius
Centripetal force equation
Fc=mv^2/r
Simple harmonic motion equations for displacement
s=Acoswt
s=Asinwt
Simple harmonic motion equations for velocity
v=-Awsinwt
v=Awcoswt
Simple harmonic motion equations of acceleration
a=Aw^2coswt
a=-Aw^2sinwt
What is meant by crosslinking
When power from a wire/fibre is picked up by an adjacent wire and creates an undesired effect
Function of non-inverting amplifier
It amplifies the input voltage by a constant amount because Vin is proportional to Vout. The output has the same polarity as the input.
Function of inverting amplifier
Vin is proportional to Vout only the output polarity has been reversed
Explain the formation of darker lines
Electrons absorb energy from photons and are excited to a higher energy level. The difference between the energy levels is equal to the energy of the photons. The electron de-excites and re-emits the photon in all directions.
Explain the dependence on the light intensity of the resistance of an LDR
Electrons in valence band absorb photons and electron jumps to the conducting band. There are positive holes left in the valence band. When the intensity of light increases there are more excited electrons in the conducting band. More charge carriers means the resistance decrease.
Difference between adiabatic and isothermal
In isothermal processes, the change in temperature is zero while in adiabatic the change in heat is zero. In isothermal expansion, thermal energy can be absorbed for an expansion whereas in adiabatic the internal energy is absorbed for expansion.
First Law of thermodynamics
Change in internal energy= Energy supplied by heating + energy supplied by doing work on gas.
ΔU=q+w
How are characteristic x-rays formed
When an electron from a inner shell is ejected from shell. This causes electrons from higher energy levels to fall into the vacant energy level and in doing so, they emit an x-ray.
Mass Defect
The difference in mass between the total mass of the individual nucleons separated to infinity and the mass of the nucleus
1 atomic mass unit
1 u is defined as 1/12 the mass of a neutral atom of carbon-12
Binding Energy
The minimum energy needed separate the nucleons in a nucleus to infinity
Decay constant
The probability that an individual nucleus will decay per unit time interval
Purpose of laminations in an iron core
To reduce the eddy currents and the thermal energy that they create in the core. To reduce energy loss
Why does the resistance increase in a copper wire when its temperature increases
There is no gap between the valence and conduction band/ no forbidden band and the number of charge carriers does not vary with temperature. Then the temperature increases there are increased lattice vibrations. These vibrations hinder the movement of electrons so the resistance increases
Faraday’s law of electromagnetic induction
The induced emf is directly proportional to the rate of change of magnetic flux linkage
Infinite Bandwidth
When the gain is constant for all frequencies of voltage
How to distinguish between non-inverting amplifiers and inverting amplifiers
Non-inverting amplifiers have the input voltage at V+ while inverting amplifiers have the input voltage at V-.
Non-inverting amplifier G = Vout/Vin = 1+ R1/R2. R1 is the resistor closest to the Vout.
Inverting amplifier G = Vout/Vin = -Rf/Rin
How does the resistance of a semiconductor decrease with an increase in temperature
The gap between the valence band and conducting band is very small. The valence band is full and the conducting band empty. When the temperature is increased, more electrons gain energy and jump to the conducting band. There are more charge carriers in the conducting band and thus the resistance decreases.
Virtual Earth
Since the open-loop gain is infinite, any small difference in V+ and V- results in saturation. Negative feedback ensures there is a very small difference between V+ and V-. In order for the amplifier to not saturate V+=V- Since the noninverting input is 0V then inverting input must also be 0V.
It is a behavior exhibited by inverting amplifier circuits as inverting amplifier circuits
Capacitance of an isolated sphere
C=4πe0r
Lenz’s Law
Any induced current or induced emf will be established in a direction so as to produce effects which oppose the change that is producing it
Relationship between the activity of a radioactive sample and undecayed nuclei
A=-λN
Explain why there is a continuous spectrum of x-ray photons produced
Because the electrons decelerate at the hard metal anode. Because of attraction from the nuclei of the metal, as the electron passes by the nuclei there is a range of decelerations (hence braking radiation). The photon’s energy depends on the magnitude of the deceleration.
What does the rate of discharge of a capacitor depend on
When the resistance over the capacitor or the capacitance of the capacitor is increased, the rate of discharge is slower.
Magnetic flux definition
It is the magnetic flux density multiplied by the area of the coil and the number of turns in the coil. The area of the coil must be perpendicular to the magnetic field.
In NMRI why are radio waves used
Because radio waves have the same frequency as the natural Larmour frequency of the protons and the protons need to vibrate in resonance.
In NMRI why are radio waves emitted in pulses
Because there must be time between the pulses for the radio frequency wave to be remitted and detected by the receiver coil.
Advantages and disadvantages of wire-pairs
Cheap, convenient. Attenuate strongly, low bandwidth,
lots of crosstalk, low security, lots of noise, and interference.
Advantages and disadvantages of coaxial cable
More expensive, less attenuation (as less emission of EM waves), higher bandwidth, less interference, little crosstalk, more secure.
Advantages of AM
Greater area covered by one transmitter because they use lower frequencies. Smaller bandwidth means more stations available. Cheaper receivers and transmitters.
Advantages of FM
Less electrical interference and noise, greater bandwidth produces better quality sound with more frequencies.
Microwave transmission
Can pass through the ionosphere to reach satellites. Bluetooth and Wifi. Must be line-of-sight except when retransmitted by satellite. 1-300GHz. Frequencies above 1GHz are considered microwaves
Space wave transmission
Sky waves with a greater frequency. Line-of-sight transmission. Can pass through the ionosphere, unlike sky waves but cannot reach satellites. FM radio in VHF and TV and mobile phones in UHF. 30-300+ MHz
Sky wave transmission
Travel almost in a straight line. May be reflected at the ionosphere worldwide transmission. Short wave radio. 3-30MHz
Surface wave transmission
Diffracts around the surface of the earth because of long wavelengths. Long-range up to 1000km. AM broadcasts in MW and LW bands. Up to 3MHz
Explain why gravitational potential energy is always negative
Because the forces of gravity are attractive so a mass will always lose potential when it gets closer to the surface of another mass. Since the potential at infinity is 0 the potential can only decrease and hence it is always negative. Work must be done to move the mass to infinity and when work is done its potential increase.
Thermal Energy
The energy transferred from one object to another because of a temperature difference (another term for heat energy)
Specific Latent Heat
The thermal energy required per unit mass to change the state without any change in temperature.
Why do most of the emitted electrons have a velocity less than v max in the photoelectric effect
Because work must be done to bring the electron to the surface of the metal so this deducts from the final kinetic energy of the electron
The shape of a velocity displacement graph for simple harmonic motion
An elliptical shape
The purpose for the copper braid in coaxial cable
To shield the signal from EM interference
To provide a return for the signal and to allow the current to flow back to the source
Photon
A packet of a discrete amount of energy of electromagnetic radiation
Photoelectric effect
When electromagnetic radiation is incident on the surface of a material and causes the emission of an electron as the electrons absorb photons
If you need to explain how the photoelectric effect is affected by the intensity of light refer to the work function or the threshold frequency of light
Radioactive decay
The spontaneous and random emission of particles from an unstable nucleus
(alpha beta gamma particles)
Line of force in a gravitational/electric field
The direction of the force experienced on a (small test mass)/(small positive test charge)
Natural frequency of vibration of a system
The frequency at which a body will naturally vibrate when there is no external resistive force acting on it
Infinite slew rate
The output changes at the same time as the input changes with no time delay
How to improve sharpness in x rays
Smaller anode area, add a lead grid to filter out uncollimated beams, make aperture smaller to increase collimation
Advantages of digital signals
Noise can be eliminated as the signal can be regenerated (removes the noise)
It has safeguards. Errors in reception are noticed and parts of the signal can be sent again
The signal can be encrypted
Signals can be transmitted over large distances
Information can be processed and stored more easily
State the effect on the transmitted signal when the sampling rate of the ADC is increased
The step width is reduced
State the effect on the transmitted signal when the number of bits in each sample is increased
The step height is reduced
What is meant by FM
It is when the frequency of a carrier wave is varied in synchrony with the displacement of an information/signal wave
What is meant by AM
It is when the amplitude of a carrier wave is varied in synchrony with the displacement of an information/signal wave
Nuclear fission/fussion
When two nuclei combine to form a single nucleus
When a single nucleus divide to form smaller nuclei
The binding energy per nucleon increases in both instances
Why is gravitational potential at a point always negative
Because gravitational forces are attractive and work must be done to increase the separation between masses and since gravitational potential at infinity is zero, the potential can only decrease when two masses approach each other (ie separation decreases)
Noise
Unwanted signal that superimposes over transmitted signal
When is a system in resonance
When the frequency of the driver is equal to the natural frequency of the system
When its amplitude is at a maximum
It absorbs the greatest possible energy from the driver
Magnetic flux density at a point
The force experienced per unit length by a long straight conductor carrying unit charge and placed at right angles to the field at that point.
Evidence for particulate nature of electromagnetic radiation
The maximum kinetic energy of electrons is independent of intensity
The maximum kinetic energy of electrons depends on the frequency
No time delay between illumination and emission and a single photon is enough to release an electron
There is a threshold of minimum frequency below which electron emission does not occur
Root mean square current
The root mean square value of an alternating current is that steady current which delivers the same average power as the ac to a resistive load
