Speed & Velocity, Scalars & Vectors Flashcards
What is speed (scalar or vector)?
Speed is scalar
- It only has magnitude.
Average speed is the distance travelled divided by the time interval.
What is velocity (scalar or vector)?
Velocity is vector
- It has magnitude and direction.
Average velocity is the displacement of an object divided by the time interval.
What is a force?
- Force is a push or pull upon an object resulting from the object’s interaction with another object.
- Whenever there is an interaction between two objects, there is a force upon each of the objects.
- When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
- Newton’s First Law of Motion states that objects with balanced forces acting on them will stay at rest or stay in constant motion.
- Newton discovered that objects will continue to do what they are doing until an unbalanced force acts on the object
Newton’s Second Law equation
F=ma
Where m is the mass and a is the acceleration. In SI base units:
mass is expressed in units of kilogram (kg)
acceleration is expressed in derived units of m/s2
force is expressed in newtons (N)
Weight & Mass
- Weight is not the same as mass.
- Mass is a measure of how much matter is in an object.
- Weight is a force acting on that matter.
- Mass resists any change in the motion of objects.
In science, the term weight has a specific meaning - which is the force that acts on a mass due to gravity.
* Weight is measured in newtons.
* Mass is measured in kilograms.
The mass of a given object is the same everywhere, but its weight can change. We use balances to measure weights and masses.
- Work is done whenever a force moves something.
- Everyday examples of work include walking up stairs, lifting heavy objects, pulling a sledge and pushing a shopping trolley. Whenever work is done, energy is transferred from one place to another.
Work equation
work=force ×distance
eg work=10 N ×2 m=20 J
- Work has the same units as energy – joules.
- This is because energy is the ability to do work. So you must have energy to do work.
- You do not have to do work if you have energy – potential energy does not do work
- Work done is equal to energy transferred
Potential energy equation
PE=m ×g×h
m is the mass in kilograms, kg
g is the gravitational field strength in newtons per kilogram, N/kg
h is the change in height in metres, m
Kinetic energy
KE=1/2 mv^2
m is the mass in kilograms, kg
v is the speed in meters per second, m/s
- All moving objects have kinetic energy (KE)
- The KE of a body depends on its:
- mass
- speed
Conservation of Energy
- Energy can be stored or transferred, but it can not be created or destroyed.
- The total energy of an isolated system stays the same.
Energy & electron volts
An electron volt is a non-SI unit of energy
It is defined as the amount of kinetic energy gained (or lost) by a single electron accelerating from rest through an electric potential difference of one volt in a vacuum
There are other equivalent definitions based on the amount of work (energy transfer) required to move one electron through a potential difference of 1 volt.
1 eV=1.6 ×10^-19 Joules
How much kinetic energy would the electron gain by time it reached the anode?
- Potential difference of 1 volt
- Electron has electro potential energy and produce kinetic energy as it accelerated towards anode.
- It has gained 1 electro volt of energy.
Atomic Structure
- Nucleus & Shells
- An atom has a central nucleus.
- This is surrounded by electrons arranged in shells
- Nucleus & Shells
- Protons and Neutrons have about the same mass of 1.67 x 10-24 grams
- Protons are positively charged
- Neutrons have no charge
- Electrons have a mass of 9.11x 10-28 or about 1/1800 of the mass of a proton or neutron
- Electrons each have a negative charge equal to the positive charge of the proton.
Proton neutron and electron: Charge, Mass and Location
Proton
Charge: +1
Mass: 1
Location: nucleus
Neutron
Charge: 0
Mass: 1
Location: nucleus
Electron Charge: -1
Mass: 0
Location: orbitals
- Volume of Atoms
- Most of the volume of an atom—greater than 99%—is in fact, empty space!
- The electrons that surround all atoms are negatively charged and cause atoms to repel one another stopping them from occupying the same space.
- Atomic Number (Z)
- The number of protons in an atom of an element is its atomic number.
- All atoms of a given element have the same number of protons
- Atoms of different elements have different number of protons.
- Atomic mass number (A)
- The mass number of an atom is its total number of protons and neutrons
- Atoms of different elements usually have different mass numbers.
Electron shells
Electrons occupy defined orbits around the nucleus in this simplified view.
* These orbits are sometimes called shells and are labelled K, L, M, N etc.
* These shells can be occupied only by certain numbers of electrons.
* The maximum number of electrons able to occupy the K-shell is 2, for the L-shell its 8, for the M-shell its 18, for the N-shell its 32 and for the O-shell its 50.
* If an electron is removed from a shell a positive ion results.
- Electron Binding
- Electrons are bound to the atom by what is referred to as binding energy.
- This energy is weaker the further the electron is from the nucleus
- This can be shown using an energy level diagram as illustrated here for tungsten (W)
Atomic basic
Electrons can move one shell to another
* An electron can move from a lower shell to a higher shell if enough energy is absorbed by the atom.
* An electron can move from a higher shell to a lower shell to get rid of excess energy.
* The transitions follow complicated rules and some transitions are simply forbidden.
Bound electrons are regarded as having negative energy
* To free and an electron from an atom the energy must be raised to zero or to a positive value
* The energy required to release an electron is termed the “binding energy”
binding energy
- The energy required to release an electron
Band Theory of Solids
- When electrons are brought together, as in a solid made up of many atoms, the orbitals of the electrons are strongly influenced by the proximity of neighbouring atoms
- This results in the electrons not occupying discrete energy levels but instead occupy energies that are within a band of energies
Valence band
Represents electrons within the material that is bound to their parent atoms no conduction in the conduction band.
What is charge?
- Electric charge is a basic property of matter carried by some elementary particles
- Electric charge can be positive (+) or negative (-)
- The unit of charge is the Coulomb
- This is a derived SI unit having base units of Ampere (A) Seconds (s): A.s
- A physical consequence of the amount of charge is that:
- Two objects with an excess of one type of charge exert a repulsive force on each other
- Two objects with an excess of opposite type of charge exert an attractive force on each other
- This force is called Coulomb Force
Coulomb force equation
F= kq1q2/R2
k is a constant ( 9 x 10’9 N.m2C’-2)
q1 & q2 are the signed magnitudes of the charges in coulombs (C).
r is the distance between the charges in meters the speed in meters per second, m/s
Static Electric Field
The electric field is defined for a charge distribution (Q) as the force that Q would exert on a positive unit charge (q =1)
Electric and Magnetic Field
- If a charge is moved at constant velocity not only is an electric field observed, but also a magnetic field
- The E and H fields move along with the charge
- The presence of a magnetic field can be detected by its effect (force) on magnets or its effect on a moving electrical charge
If the charge is accelerated, the E and H fields lag behind the charge
This produces a distortion in the electric field lines that moves outward from the charge with a finite, but large, velocity.
This distortion is EM radiation.
EM radiation is produced by accelerating a charged particle (this is not the only way!)
Electromagnetic Radiation
Electromagnetic radiation transports energy through space as combinations of electric and magnetic fields
Examples: Radio waves, radiant heat, visible light, X-ray and gamma radiation
Oscillating charge
Perpendicular
reverse together
energy is transmitted through space
Electromagnetic Spectrum
radio
microwave
infrared
visible
ultraviolet
x-ray
gamma ray
Wave-Particle Duality
- The interactions of different kinds of EM radiation are difficult to understand.
- Some are explained only if they are assumed to be particles, while others are explained only by theories of wave propagation
- This does not mean that EM radiation is either made up of particles or waves – it exhibits both types of behaviour depending on how it is viewed
Wave Concept of EM
EM is propagated through space in the form of waves.
EM travels at the speed of light (3 x 108 m/s) in a vacuum
Particle Concept of EM
- Short EM waves (such as X-rays) react with matter as though they were particles
- Quanta
- Photons
E x hu
energy (Kev)
Planck’s constant
frequency
Electric Circuits
- Electric current is the flow of charge (electrons in this case)
- Current is the number of charges per unit time passing through a boundary
- Conventional current flow is defined to be in the opposite direction to the flow of the electrons
Electric Circuits: Resistance
R= P L/A
R resistance in ohms (Ω)
L length in metres (m)
A area in square metres (m2)
ρ resistivity ohm metres (Ωm)
Electric Circuits: Ohms Law
V= IR
- V voltage in volts (V)
- I current in amperes (A)
- R resistance in ohms (Ω)
Electric Circuits: Power
P= IV
- P power in watts (W)
- I current in amperes (A)
- V voltage in volts (V)
Electric Circuits: energy
E= IVt
Capacitors
Capacitors are used to store electrical charge.
By applying a voltage to a capacitor and measuring the charge on the plates, the ratio of the charge Q, in coulombs, to the voltage V, in volts, will give the capacitance value of the capacitor in units of farad.
- Which one of these is NOT a scalar quantity?
a. distance
b. time
c. displacement
d. density
e. energy
c. displacement
- Which one of these is NOT a vector quantity?
a. velocity
b. acceleration
c. temperature
d. force
e. Coulomb force
c. temperature
- In science weight is measured in _____ and mass is measured in _____ using SI units. Match the words in the statement.
a. kilograms, newtons
b. newtons, pounds
c. kilograms, pascals
d. newtons, kilograms
e. kilograms, kilograms
d. newtons, kilograms
- A block of metal has a mass of 1.2 kg and therefore weighs approximately 12 newtons on the Earth. What is the block’s weight and mass on the Moon where the acceleration due to gravity is 1/6 that of Earth’s. Match the correct mass and weight from the following
a. 2 kg, 2 N
b. 1.2 kg, 1.2 N
c. 2 N, 1.2 kg
d. 2.4 N, 24 N
c. 2 N, 1.2 kg
- A force of 250 N is used to push a car a distance of ¼ of a mile. What is the work done? (1 mile is approximately 1.6 km)
a. 10 x 10’5 J
b. 10000 J
c. 1 x 10’5 J
d. 1 x 10’5 W
1 x 10’5 J
- What is the potential energy gained by a bag of sugar having a mass of 1 kg if it is raised to a height of 10 m directly above its starting position? (use g = 10 N/kg)
a. 100 mJ
b. 5 J
c. 100 J
d. 1000 J
e. 4 J
c. 100 J
- What is the kinetic energy of an electron that has been accelerated through a potential difference of 7.5 kV expressed in electron volts?
a. 7.5 eV
b. 750 V
c. 7.5 keV
d. 75, 000 V
e. 750, 000 eV
c. 7.5 keV
- Which one of the following statements is true?
a. An electron has a mass approximately 1800 times that of a proton
b. A proton has a mass which is approximately double that of a neutron
c. A neutron has a mass which is approximately 1800 greater than an electron
d. An electron has zero mass
c. A neutron has a mass which is approximately 1800 greater than an electron
- An electrical resistor has a value of 1 MΩ which is equal to
a. 1 × 10’9 Ω
b. 1 × 10’6 Ω
c. 1 × 10’3 Ω
d. 1 × 10’2 Ω
e. 1 × 10’12 Ω
1 × 10’6 Ω
Accounting for the masses of the nucleus and the electrons of an atom what approximate percentage of the volume of an atom is made up of empty space?
a. 10%
b. > 99%
c. 0%
d. 50%
e. < 99%
. > 99%
- To free an electron from an atom energy must be added which is equal to or greater than its ______ energy. Match the correct word.
a. orbital
b. shell
c. binding
d. nuclear
e. electron
binding
- In an insulator at room temperature the valence band is ¬¬¬____ and the conduction band is _____ of electrons. Match the correct words.
a. full, empty
b. full, full
c. empty, full
d. empty, empty
a. full, empty
- The Coulomb force between two isolated charges is _____ to the product of their magnitudes and _______ to the ______ of the distance between them. Correctly match the following words to the statements.
a. inversely proportional, proportional, square root
b. inversely proportional, inversely proportional, square
c. proportional, proportional, square
d. proportional, inversely proportional, square
d. proportional, inversely proportional, square
- A charged particle moving with constant velocity produces
a. only an electric field
b. electric and magnetic fields
c. only and magnetic field
d. electromagnetic radiation
b. electric and magnetic fields
- EM radiation is produced by which one of the following
a. a bound electron orbiting the nucleus of an atom
b. oscillating the position of a free (unbound) electron in space
c. cooling an electron to absolute zero
d. moving an electron at a constant velocity
b. oscillating the position of a free (unbound) electron in space
- The wavelength of diagnostic X-rays is in the region of:
a. 0.1 to 1 micrometres
b. 0.1 to 10 nanometres
c. 100 to 1000 angstroms
d. 0.1 to 10 angstroms
d. 0.1 to 10 angstroms
- X-rays fall between ¬_____ and _____ on the electromagnetic spectrum. Correctly match the following words
a. radio waves, infrared
b. infrared, Gamma rays
c. Ultraviolet, Gamma rays
d. Infrared and ultraviolet
c. Ultraviolet, Gamma rays
- Which one of the following gives the correct volume for a cube measuring 0.5 cm × 0.5 cm × 0.5 cm.
a. 0.125 cm’2
b. 0.25 cm’3
c. 0.125 cm’3
d. 1.25 cm’3
e. 0.125 cm’-3
0.125 cm’3
- If 3 coulombs of charge, moving in the same direction, passes a boundary in a conductor every 6 seconds what is the current in SI units
a. 0.5 A
b. 2 A
c. 1 A
d. 0.5 C
e. 10 V
0.5 A
- Which one of the following most closely matches the resistance of a copper wire 10 m long with a diameter of 2 mm? (The resistivity of copper is 1.7 × 10-8 m).
a. 54.1 mΩ
b. 0.5 Ω
c. 5.4 Ω
d. 20 Ω
54.1 mΩ
- A voltage of 9 v is applied across a resistor of 1 kΩ for 10 seconds. Which one of the following gives the correct values for i) the current that flows through the resistor during this time ii) the power dissipated by the resistor iii) the total energy expended over this time
a. 9 mA 81 mJ, 0.81 W
b. 9 Ω, 81 J, 0.2 V
c. 9 mA, 81 mW, 0.81 J
d. 10 mA, 81 W, 1.5 J
c. 9 mA, 81 mW, 0.81 J
- A capacitor stores 100 C of charge. If the voltage across the capacitor is 100 V, what is the capacitance of the capacitor?
a. 1 µF
b. 1 µH
c. 10 µF
d. 1 pF
1 µF
