Bmat section 2 physics Flashcards
Describe how insulators like a cloth and a plastic rod can be charged by friction. and what is this process known as, why does it have this name
If a plastic rod and a cloth are rubbed against each other, one of the two will lose electrons to the other. If the rod loses electrons to the cloth, it will have less electrons and therefore will be positively charged, and the cloth will be negatively charged as it will have more electrons. This is called static electricity. it is static because, the electrons cannot move in the cloth/ rod as they are insulators, so we can say that the insulators “HOLD” the electrons
hazards of static electricity
it can cause a spark which can be dangerous
an example is when an aircraft is being refueled.
lightning is also a hazard of electrostatics
how is sparkling in static electricity prevented
by earthing
in the example of the refueling of an aircraft, both the aircraft and the truck are earthed and this prevents any charges from building up and leading to a spark
unit for charge
coulombs
conservation of charge rule
charge can be conserved but cannot be created nor destroyed
can positive charges move in solids? give a reason for your answer
no they can’t, because they are held in place by other atoms.
effect of distance on electrostatic forces between charged objects
As the distance between charged objects increase, the electrostatic force between the objects decrease (become weaker) and vice-versa
applications or uses of electrostatics
can be used in photocopier machines
can be used in laser printers
can be used in electrostatic spray painting
what happens when a live wire touches a metal casing that has been earthed
a large current will flow to the Earth and
blow the fuse, disconnecting the appliance from the power supply.
This protects users from electric shock. This also protects the wiring of the
circuit from overheating and causing a fire
types of current and their definitions
Direct current: in direct current, the flow of electric charge is in only one direction
Alternating current: in this type of current, the flow of electric charge periodically reverses direction
conductors and insulators, their definitions and examples
conductors are materials that permit electrons to flow freely from particle to particle. examples are metals, the human body, aqueous solutions…
inductors are materials that impede the free flow of electrons from atom to atom
and molecule to molecule. examples are plastics, paper, and dry air.
formula for current
charge/time
formular for resistance
voltage/current
formula for voltage(linking energy and time)
energy/time
formula for power(linking current and voltage)
current* voltage
the formula for energy transfer
power*time
the rule for current in a parallel circuit
the current in the branches of a parallel circuit add up to the total current leaving the cell
the rule for current in a series circuit
the current is the same all around the series circuit
what does the potential difference (voltage) tell us
the amount of energy transferred for each coulomb of charge moving through an electrical circuit
voltage in a series circuit
the voltage is the same across a series circuit, however, when they are more than one appliances, then the potential difference is shared between the appliances
potential difference in parallel circuits
for components connected in parallel, the potential difference across each component is the same as the potential difference of the cell
ELECTROMOTIVE FORCE equation
POWER/CURRENT
when can we say an ammeter has zero error
when an ammeter displays a reading while not connected to a circuit
Which waves transfer the most energy
Waves with the short wavelength and high frequency
Which colour between white and black is better at absorbing infrared
Black
Which colour between white and black is better at emitting infrared
Black
Which colour between white and black is better at keeping people warm in the winter
White
Homozygous
When an organism has two identical alleles(versions) of the same gene
Heterozygous
When an organism has different alleles(versions) of a gene
Charge on an electron
Charge on a proton
-1.610^19
+1.610^19
Potential difference (relating to work done and charge)
Work done/charge
What unit is emf measured in
Volts
Ntc thermistors
Resistors with a negative temperature coefficient, which means that the resistance decreases as temperature increases
LDRs
A resistor with resistance that depends on the might intensity of light that falls on it. It’s resistance decreases as light intensity increases
What happens when a voltage is applied in reverse in a diode.
When does a diode conduct forward current instantly
The diode conducts no current at all
When voltage is applied across the anode to the cathode
Electric power formula
Current Voltage= current^2 resistance = voltage ^2/resistance
Energy transfer formulae
Power *time
Voltage formula(that links energy with charge)
Energy / charge
Where does thermal energy always flow from? and when does the transfer of thermal energy happen
A region of higher temperature to a region of lower temperature
When two objects of different temperatures are placed together
What happens when two objects of different temp. Are placed together?
When is there no thermal equilibrium
A thermal equilibrium is obtained , where the hotter object will decrease in temperature and the colder object will increase in temperature until the temperature is the same
When there is a change of state of the objects
Thermal energy lost by the hot object is equal to?
The sum of the thermal energy gained by the colder object and the energy loss to the surroundings
Conduction
When heat is transmitted through a medium from one particle to another through vibrations about fixed positions
Examples of thermal conductors
Metals
Thermal insulators and examples
Materials that transfer thermal energy slowly
Gases, plastic , wood
Name four factors that affect conduction
Cross sectional area of the material (increase means greater rate of conduction)
Temperature difference across material(greater temperature difference means greater rate of conduction)
Thermal conductivity of material per unit thickness
Length or thickness of material( longer distance means slower rate of reaction)
Formula for rate of conduction
Change in energy/ change in time=
kA (T1-T2/ l)
In which states do convection normally occur
In fluids (gases and solids )
Describe the process of convection
Liquid and gases expand when heated as density decreases with increasing temperature
The fluids in hot areas are less dense than those in cold areas, so they rise into the cold areas. The denser cold liquids falls into the hot areas
In this way , convection currents are set up
Does radiation require any medium
No
If an object is a good absorber , then it’s a good…
Emitter
Which objects emit and absorb electromagnetic radiation
All objects
Which colour objects are the worst and best absorbers
Shiny and white objects are the worst as they reflect all visible wavelengths , while darker objects are the best
factors that affect the rate of absorption and emission of thermal radiation
Colour
Surface texture
Surface area
Temperature
Dull, matte and rough objects are good…… and poor …..
Smooth surfaces are good ….. and poor……
Absorbers and emitters
Absorbers and emitters
Which objects radiates heat energy faster , a thin flat object or a fat object
A thin flat object cos it has a larger surface area
Specific heat capacity and equation, with units
The amount of energy required to raise the temperature of a unit mass by 1 degree Celsius or 1 Kelvin, without any change of state
C= Thermal energy / mass*change in Temperature
J kg^-1
Waves
Phenomenon in which energy is transferred from one place to another through vibrations, without the transfer of particles
Transverse waves and examples
Longitudinal waves and examples
Waves that travel in a direction perpendicular to the direction of vibrations
Examples are electromagnetic and water waves
Waves that travel in a direction parallel to the direction of vibrations
Examples are sound waves
Wave equation
Wavespeed= frequency * wavelength
Frequency equation
F= 1/t
Period
Si unit
Time taken to generate one complete wave
Second
Wavelength
Distance between two successive crests or two successive troughs in a wave
Amplitude
Magnitude of the maximum displacement from the rest position of the wave
Wavefronts are normally not straight lines , true or false
False
When does refraction occur
When waves travel from one medium to another
What happens to the frequency , wavespeed and wavelength when a wave bends towards the normal
Frequency stays constant
Wavespeed decreases
Wavelength decreases
Laws of reflection
The incident ray , reflected ray and normal lie on the same plane at the point of incidence
Angle of incidence is equal to the angle of reflection
Properties of images in a plane mirror
They are virtual
Upright
They are the same size as the object
They are laterally inverted
They are the same distance behind the mirror as the object is in front of the mirror
Difference between a cone of light problem and large object problem
The lights rays start at the same point on the object and end at different points on the eye for cone of object problems while
the light rays start at two different points on the object and end at the same point on the eye for large object problems
Which of reflection, refraction and refraction changes frequency bog a wave
None of them
Why does light bend when it enters another medium
Because the speed of light changes when it enters another medium
Refractive index
The ratio of the speed of light in vacuum to the speed of light in a medium
Speed of light
3*10^8 m/s
What happens when a light ray travels from a medium of lower refractive index to a medium of higher refractive index
It bends towards the normal
Angle of deviation
The angle between the incident and the refractive ray
Laws of refraction
The incident ray, refracted ray and the normal at the point of incidence all lie on the same plane
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant(snells law)
There are two formulas for refractive index , what are they
n= speed of light in vacuum / speed of light in medium
n= sin I/ sin r
Do sound waves require a medium to travel through , if so why?
Yes they do
They are mechanical waves
What determines the loudness of sound waves
What determines the pitch of sound waves
Amplitude
Frequency
In which states do sound travel the fastest and slowest and why is this
Fastest in solids , slowest in gasses
Because particles are denser in solids(compressions and rarefractions are transmitted faster in denser media)
What is the human audible frequency range
Between 20Hz to 20kHz
Ultrasonic frequencies
Infrasound frequencies
Human audible frequency above 20kHz
Below 20Hz
Speed at which electromagnetic waves travel in a vacuum
The speed of light , I.e (3*10^8m/s)
Properties of EM waves
All EM waves transfer energy from one place to the other
They are transverse waves
They can travel through a vacuum
In a parallel circuit , the overall resistance is ……. Than the resistance of the individual resistors
Smaller or less than
What do decomposers use for respiration
Oxygen
Proteases can break down other enzymes , explain why
Enzymes are made from proteins , and proteases break down proteins , so proteases can break down enzymes
Nuclides
Type of atom whose nuclei have specific number of protons and neutrons, characterised by the energy state of the nucleus
Radioactive decay
When the nucleus of an unstable isotope gives of radiation to become stable
Is radioactive decay random? If so why?
Yes it is
Because scientists cannot determine when a particular nucleus will decay
Activity
Si Unit
Rate a which a source of unstable nuclei decay
Becquerel(Bq)
Equivalent of 1 becquerel
1 decay per second
Device used to measure activity
Geiger-Muller tube
Count rate
Number of decays recorded each second by a detector
Types of radiation that can be given out by an unstable nucleus
Alpha particles
Beta particles
Gamma radiation
Neutrons (rare tho)
Alpha particles (decay)
These are in the form of a helium atom
I’m alpha decay, a helium atom is ejected or released
The two Rules for alpha decay
The atomic number decreases by two
The mass number decreases by 4
How Beta particles (decay) are formed and what happens during beta decay
They are formed inside the nucleus when a neutron change into a proton and an electron
In beta decay, an electron is ejected from the nucleus at a very high speed
Two Rules for beta decay
Atomic number increase by one
Masa number does not change
Rule for gamma radiation
Both the atomic and mass number are not changed at all
Penetrating ability
How easily a type of radiation can pass through materials
In general , a greater mass results to
…… ionising power
…….penetration power
Greater
Lower
Equation of motion
V^2-u^2= 2as
Term given to when an object changes shape
Deformation
Types of deformation and their meanings
Elastic deformation : reversed when the force is removed
Inelastic deformation: is not fully reversed when force is removed
Hooke’s law
Force = spring constant *extension
Limit of proportionality
A measure of the stiffness of a spring up to it’s limit of proportionality
Shape of a force extension and type of deformation graph when
Stretched below limit of proportionality
Stretched above limit of proportionality
Linear and elastic deformation
Non linear and i elastic deformation
What does the gradient of a force- extension graph before the limit of proportionality represent
The spring constant
Energy stored in a spring
Elastic potential energy
Formula of elastic potential energy
E= 0.5Kx^2
Or
E=0.5 Fx
What devices are usually used to measure
weight
Mass
Spring balance/ compression balance
Beam balance/ electronic balance
