Physics 100
The electrostatic force is another example of
"action at a distance."
One coulomb of positive charge will
"cancel" 1 coulomb of negative charge.
Generator
(opposite of a motor) converts mechanical energy into electric energy by coil motion.
Coulomb's force between 2 point charges 10µC and 5µC placed at a distance of 150cm is
0.2 N
Electron charge
1.6 x 10^-19 coulombs
Infrared radiation (IR)
10^12 hertz to 4x10^14 hertz (400,000,000 megahertz) used in wireless remote-control units, ordinarily the main component of heat radiation.
the electrostatic force between an electron and a proton is about
10^39 times as large as the gravitational force between them.
The resistance of an electric heater is 10 Ohms when connected to 120 volts. How much energy does it use during 30 minutes of operation?
2592000
The low beam on a car "consumes" 40 Watts. The voltage is 12 volts. What is the current in the low beam?
3.33 Amps
X-ray
3.6×1018 hertz to 12×1018 hertz, bones absorb x-rays better than soft tissue such as muscle or fat.
Gamma rays
3×1019 hertz to beyond 1023 hertz, very penetrating and potentially harmful.
Visible light
4.0 x 1014 to 7.5 x 1014 Hz, narrow band, source of colors of light, White light - combination of all frequencies (colors) of light AND Black - no visible light reaches the eye.
A 20 Amp circuit breaker "trips" (turns the circuit off) if the current in the circuit exceeds 20 Amperes. If the voltage of the circuit is 120 Volts, how low does the resistance have to be to "trip" the breaker?
6 OHMs
Ultraviolet (UV) radiation
7.5×1014 hertz to 1018 hertz, part of sunlight is responsible for suntans and sunburns
During 30 seconds, 250 Coulombs of electric charge flow through a microwave oven. What is the electric current?
8.3 Amps
The resistance you feel when pushing a piece of iron into a coil involves A. repulsion by the magnetic field you produce. B. energy transfer between the iron and coil. C. Newton's third law. D. resistance to domain alignment in the iron.
A
A positive ion is formed when 1.a neutral atom gains an electron. 2.a neutral atom loses an electron. 3.a negative ion loses an electron. 4.All of the above.
A neutral atom loses an electron
Two charged objects exert forces on each other. The sizes of both forces will increase if 1.the objects are brought closer together. 2.the charge on one of them is increased. 3.the charges on both of them are increased. 4.All of the above.
All the above
Electric current is measured in
Amperes (amps) A
Describe the differences and similarities between gravitational and electrostatic forces
Both the gravitational and the electrostatic force are inversely proportional to the square of the distance between the two bodies, but gravitational forces are always attractive, whereas, electrostatic forces can be both attractive and repulsive
Semiconductors
Characteristics of both insulators and conductors, examples - silicon and germanium, useful in computer chips.
Electric motors
Converts electrical energy into mechanical energy of rotation.
Charge unit
Coulomb, C
An inherent physical property of certain subatomic particles that is responsible for electrical and magnetic phenomena is an
Electric charge
The word electricity comes from
Electron
AC (alternating current) voltage
Electrons are moved first in one direction and then in the opposite direction, alternating back and forth about fixed positions. Think batteries.
True or False? According to the law of reflection, if the angle of incidence of a ray striking a mirrored surface is 35°, then the angle of reflection of the ray leaving the surface is 55°.
False
True or False? An electrostatic precipitator uses an electric field to make it rain.
False
electric field
Force per unit charge in units; causes any charged object to experience a force, represented by arrows forming (electric field lines).
silicon and germanium are
Good Semiconductors
Rubber and air are
Good insulators
Conservation of charge
In any charging process, no electrons are created or destroyed. Electrons are simply transferred from one material to another.
As a wire becomes thinner, what happens to the resistance?
It gets becomes higher.
electric dipoles
Molecules that have a little more negative charge on one side of the molecule than on the other.
All matter contains both positively and negatively charged particles. Why do most things have no net charge?
Most things have equal numbers of protons and electrons making the net charge zero.
Polar molecules
Net negative charge displaced to one side of the net positive nuclear charge, example water.
The force on q1 is equal and opposite to the force on q2 by
Newton's third law of motion
Resistance Unit of Measure
Ohm (1 ohm)= 1 volt per ampere
Coulomb's Law
The force acting on each of two charged objects is directly proportional to the net charges on the objects and inversely proportional to the square of the distance between them.
Two electric power supplies have a maximum power output of 100 Watts. One of the supplies produces a voltage of 6 volts while the other produces a voltage of 12 volts. What is true of the maximum current outputs of the two supplies?
The maximum current of the 6V supply is twice as big as the maximum current of the 12V supply
True or False Electric current is a flow of electric charge.
True
True or False? All three principal types of particles found in atoms are electrically charged.
True
with F in newtons, q1 and q2 in coulombs, and d in meters.
Units for Coulomb's Law
An electric current is
a flow of charged particles
A positive ion is formed when 1.a neutral atom gains an electron. 2.a neutral atom loses an electron. 3.a negative ion loses an electron. 4.All of the above.
a neutral atom loses an electron.
superconductors
acquire zero resistance (infinite conductivity) to the flow of charge.
Earth
acts as a huge magnet (has a magnetic field) moving charges within the molten part of Earth.
electrostatic precipitator
air-pollution control device
Permanent magnet
alignment of domains remains once external magnetic field is removed.
Temporary magnet
alignment of domains returns to random arrangement once external magnetic field is removed.
When you buy a water pipe in a hardware store, the water isn't included. When you buy copper wire, electrons
are already in the wire.
Magnetic fields
are produced by two kinds of electron motion.
Negative Ion
atom gaining one or more electrons, has negative net charge.
Positive Ion is an
atom losing one or more electrons, has positive net charge.
This force between charged objects is extremely important in the physical world, particularly at the atomic level. It is this interaction that holds
atoms together and makes it possible for them to exist.
The (gravitational) force between two bodies because of their masses is always an
attractive force
the (electrostatic) force between two bodies from their electric charges can be
attractive or repulsive, depending on whether or not they have opposite charges.
Upon entering a medium in which the speed of light is 1.5 ´ 108 m/s from a medium in which the speed of light is 2.0 ´ 108 m/s, an oblique ray will 1.be bent away from 2.be bent toward 3.travel along 4.travel perpendicular to 5.remain undeviated with respect to ● the normal to the interface between the two media.
be bent toward
Electric field
can travel through a circuit at nearly the speed of light. (electrons travel very slowly through a wire).
Transformer
consists of two separate coils of wire in close proximity. An AC voltage is applied to one of the coils
Electromagnet
contains coils (long wires wrapped in the shape of a cylinder, often around an iron core) can increase electromagnetic force by wrapping more coils around the cylinder and using a larger electric current.
The SI unit of measure of an Electric charge is
coulomb (C)
When you double the voltage in a simple electric circuit, you double the
current
insulator
does not readily allow the flow of charges through it.
The physical property possessed by certain particles that is responsible for electrical and magnetic phenomena is _________________.
electric charge
DC ( direct current) voltage
electric field travels in one direction. Think Wall socket.
A charged particle creates an electric _____________ in the space around it.
field
Magnetism
first observed in a naturally occurring ore called lodestone. the north-seeking part of a magnet is called its north pole, and the south-seeking part is its south pole.
Parallel circuit
forms branches, each of which is a separate path for the flow of electrons.
Metals are
good conductors
Fuses and Circuit Breakers
help protect current overload.
Electric potential energy is measured in joules. Electric potential, on the other hand (electric potential energy per charge), is measured
in Volts
Conservation of charge
in any charging process, no electrons are created or destroyed. Electrons are simply transferred from one material to another.
Electrical current
is the flow of charges particles
North Pole and South Pole
like poles repel; unlike poles attract.
Radio waves
lowest frequency EM waves, from less than 100 hertz to 1 billion hertz or 1000 megahertz, communicating, space and satellite communication.
Magnetic domains
magnetized clusters of aligned magnetic atoms.
Ammeter
measures electric current
Ferromagnetic
metals that are strongly attracted by magnets (iron, nickel, and certain other metals).
conventional current
move from positive terminal towards the negative terminal.
Electron flow
move from the negative terminal toward the positive terminal.
Diffuse reflection
occurs when light strikes a surface that is not smooth and polished, scatter in all directions.
According to Coulomb's law, a pair of particles that are placed twice as far apart will experience forces that are
one-quarter as strong.
Resistance (R)
opposition to current flow, measured in ohms, affected by composition, length , diameter and temperature.
Direction of the Magnetic field from a current carrying wire
perpendicular to the direction the current is flowing.
Many molecules—H2O, for example—are electrically_____________in their normal states
polarized
When you brush your hair and scrape electrons from your hair, the charge of your hair is
positive
Rubbing glass with silk causes the glass to acquire a net
positive charge
Alternating current in a coil
produces a magnetic field that oscillates, polarity of an electromagnet is reversed.
Charge is represented by
q
Conductor
readily allows charges to flow through it, usually metals.
Like charges _______________ ; unlike charges _______________.
repel, attract
Magnetic field lines
show the shape of the electric field
Series circuit
single pathway for electron flow.
Specular reflection
smooth surface, familiar type that we see in a mirror or in the surface of a calm pool of water.
Law of reflection
the angle of incidence equals the angle of reflection.
If one charge is negative and the other positive, then the force is negative, indicating an attractive force. If the distance between two charged objects is doubled, then
the forces are reduced to one-fourth their original values.
When two similarly charged combs are suspended from threads, they
they push each other apart. Just remember this simple rule: like charges repel, unlike charges attract.
Consider a lamp powered by a battery. Charge flows
through both the battery and the lamp.
Amount of diffraction depends on
wavelength of the wave compared to the size of the obstruction that casts the shadow.