Unit 1 Flashcards
Vector quantity
a physical quantity that has both magnitude and direction
Magnitude
the distance of a quantity from zero
Physical quantity
a property of a system that can be quantified by measurement
Direction
orientation or path of an object’s motion
Examples of vector quantities
displacement, velocity, momentum
System
collection of objects that are being studied together (e.g. sled and person on sled, single electron interacting with EM field)
Open system
Can exchange both matter and energy with surroundings (e.g. human body (waste and energy, such as food and oxygen, is transferred))
Closed system
Can exchange energy with surroundings but not matter (e.g. covered pot on stove with boiling water (heat can transfer but water cannot))
Isolated system
neither exchanges matter nor energy with surroundings (e.g. insulated water bottle (neither heat nor matter is exchanged with surroundings))
Force
when an object experiences a push or pull that causes a change in its motion. Force is a vector quantity, having both magnitude and direction
Equation for force
F=ma
-a: acceleration (m/s^2)
-m: mass (kg)
direction of acceleration is always same as direction of force
Gravitational force
force object experiences due to gravity, produces constant acceleration of 9.8 m/s toward surface of earth
Energy
the capacity to do work and exert force that causes and object to move or change its state, measured in Joules (J) (e.g. potential, kinetic, electrical, thermal, etc.)
Kinetic Energy (KE)
the energy of an object that is associated with its motion (e.g. throwing a ball, shooting arrow, falling, flying airplane) (never negative)
Formula for Kinetic Energy
KE=1/2mv^2
-m: mass (kg)
-v: velocity (m/s)
Potential Energy (PE or V)
the energy stored in an object due to its location relative to a specific reference point (e.g. raised object, dynamite, drawn bow, stretched spring, battery, etc.)
Law of Conservation of Energy
the total energy of an isolated system remains constant (Etot). An isolated system’s kinetic energy changes as the magnitude of its velocity changes, while its potential energy changes as its position changes.
Total Energy equation
Etot= KE + Vr
kinetic + potential energy
Electrical force (F(r))
the attractive or repulsive force that exists between two objects, the force that charged particles exert on each other. Charge of a particle has both sign and magnitude.
Charge of negatively charged particle
-1.602x10^-19 C
Charge of positively charged particle
1.602x10^-19 C
Electrical force equation (F(r))
F(r)= (q1q2)/4piE0r^2
-q1: charge on 1st particle
-q2: charge on 2nd particle
-E0: permittivity of vacuum (8.854x10^-12)
-r: distance between particles
Permittivity of a vacuum
A measure of how dense of an electric field is permitted to form in response to electric charges, relates units for electric charge into length and force
Electric field
the physical field that surrounds electrically charged particles. Charged particles exert attractive forces when opposite signs and exert repulsive force when same signs
Coulomb’s law
the greater the magnitude of the charges, the greater the force
Formula for Coulombic Potential Energy (V(r))
V(r)= (q1q2)/4piE0r
Coulombic Potential Energy (V(r))
the stored energy of a system of two charged [articles interacting, varies as distance between particles, r, varies
How Coulombic potential changes with same/opposite sign particles
V(r)>0 when same sign
V(r)<0 when opposite sign
Coulombic force
F(r)= -d(V(r))/dr (negative first derivative of V(r))
or
F(r)= (q1q2)/4piE0r^2 (positive=repulsive, negative=attractive)
Electric field lines
point radially outward from a positive charge and inward to a negative charge, never cross, strength of field is related to number of lines per unit
Force of electric field
F=qE
-q: charge of particle
-E: electric field vector (N/C)
Cathode-ray experiment
J.J. Thomson, put metal cathode and anode in an enclosed and evacuated tube, made cathode rays emit from cathode (negatively charged) into anode (positively charged) with hole in center, causing them to go in straight line between electric field plates. With electric field turned on, the cathode-ray was deflected in opposite direction of applied E field. Magnetic field deflected cathode-rays back to center. Different metal cathodes gave same results.
Results of cathode-ray experiment
-Because rays could be deflected by magnetic field, Thomson concluded the particles were charged.
-By measuring deflection of cathode rays in both electric and magnetic fields, was able to calculate charge-to-mass ratio of particles.
-Cathode ray behaved as negative particles.
-Atoms of different elements must contain both negative and positive charges
Cathode
negatively charged electrode by which electrons enter a device
Anode
positively charged electrode by which electrons leave a device
Electrode
a conductor through which electricity leaves or enters an object, substance, or region
Millikan oil-drop experiment
Began with a chamber with two parallel metal plates, and fine mist of oil droplets are sprayed though hole in top plate. Air is ionized, allowing electrons to attach to oil droplets and give them negative charge. By adjusting the voltage applied to the plates, the electric force acting on a droplet can be balanced against the gravitational force, causing it to remain suspended in midair.
Results of millikan oil-drop experiment
-by measuring the voltage needed to suspend a droplet and knowing its mass, millikan could calculate charge of electron (-1.602x10^-19)
mass-to-charge ratio
mg=qE
-m: mass of particle (kg)
-g: force of gravity
-q: charge of particle
-E: force of electrical field
J.J. thomson’s plum pudding model
electrons were embedded in a diffuse positive matrix of positive charge
Rutherford’s alpha particle (gold foil) experiment
positively charged particles (alpha (He2+)) were fired at thin sheet of gold foil. most particles passed straight through, but some were deflected at large angles of 90 to 180 degrees, leading to conclusion that atoms have a tiny, dense, positively charged nucleus at their center
