Physics Exam 3 Content

what is the difference between electrostatic and electricity

electrostatic: slow moving or charges are at rest

electricity: fast moving

who discovered electricity

Benjamin Franklin

what is the significance of the Baghdad Battery mystery

because a clay pot and its content (had a cathode in it) were able to produce an electric current

why are dams having a height difference important in terms of transformation of energy

a height difference is necessary so that we can have a fall (high potential energy here). when it is moving, this is work. the water can flow through turbines to turn mechanical energy into electric energy

what is a battery

a device that uses chemical energy to separate positive and negative charges, producing a potential difference between its terminals

what does the potential difference in a battery create

a current (needs to be moving fast enough)

does there need to be a big or small potential energy difference for electric current?

there needs to be a high potential difference for electric current

how does a flashlight work

it has a battery, switch, and lightbulb. the switch breaks to circuit, creating the on and off effect. when the switch is “open”, the circuit is broken=no light. when the switch is “closed”, electrons can flow through the circuit=light

which side has the greater potential energy

the positive side

how do you draw a capacitor vs a resistor

what is the direction of electron current flow

it goes from the negative terminal to the positive one

what is the direction of conventional current

opposite of electron current so positive to negative side

what is the definition of electric current (formula)

what is 1 ampere (A)

1 ampere = 1 C/s

describe the movement of electrons in a conductor

they move in random motion/have free movement. there is some resistance/lots of collisions (it is hard for the electron to enter)

compare the drift speed vs the electric signal propagation in a conductor

drift speed is low due to collisions and resistance BUT electric signal propagates more quickly

what will happen to the drift speed of electrons if you increase the surface area

there is more space→less collisions→electron drift speed will increase

if the drift speed of electrons is so slow, how does the light turn on in an instant?

electron drift is limited by collisions to 10^-4 m/s, but when electrons move away from the battery, they exert a force on their neighbors→they all move in the same direction→the effect is the electrons move through the wire at nearly the speed of light

how do you find number of electrons if you only know charge

what is epsilon equal to in this context

it is battery emf but it is the same as voltage

how do you find work of electric current

describe the direction of conventional current vs flow of electrons

current: + to -

electron: - to +

how are velocity and current the similar

they are both a unit over time (m/s vs C/s)

charges inside the conductor oppose or match the outside

oppose

how does surface area affect flow of electrons

increase in surface area increases the flow of electrons

what is a resistor

a passive two-terminal electric component that limits or regulates the flow of electrical current in a circuit

why does a wire to a home require need to be thicker vs a phone charge

the home wire has a larger charge so needs a larger surface area to prevent electron collisions

describe the motion of electrons in metal wires

they move with ease and freely BUT they experience resistance to their motion

what is needed for electric current to flow through a resistor

a potential difference

what is the difference between resistance and required potential difference for electron flow

the greater the distance the greater the required potential difference

what is Ohm’s law

V=IR (relating voltage to the current)

can Ohm’s law be applied to all materials

nope, it can only be applied to some materials, like metallic conductors. not every material is good with voltage

based on Ohm’s law, what is the relationship between voltage and current

they are proportional (V=IR). if current increases, voltage increases

what is SI unit for Ohm’s

Ohm=volt/ampere

what does resistance measure

how easily electrons flow through an electrical component

how do we find resistance using resistivity

what is the definition of resistivity

The material quantity that characterizes the resistance of a given material. it considers the geometry of the component and its properties.

which has a greater resistivty: conductors or insulators

insulators have a greater resistivity while conductors have a lower resistance

in general what is the relationship between resistance and temperature? is this the same for all materials

the resistance goes up as temperature goes up due to thermal effects, but semiconductors actually have decreased resistivity as temperature increases

what are semiconductors

a material that can conduct electricity under certain conditions but also blocks it in others (not a full conductor but not a full insulator)

what classifies a superconductor

a material that has a resistivity that drops to zero at a finite temperature: critical temperature

describe the relationship between attraction and repulsion in superconductors

it is happening at the same time (think of bullet trains where it creates that levitating effect)

are superconductors the same as semiconductors

IMPORTANT: nope!!! both materials conduct electricity, but superconductors can conduct electricity with ZERO resistance at very low temperatures. Semiconductors have a conductivity that falls between conductors and insulators. the electrical flow is very controlled depending on temperature and doping levels (aka there will be resistance)

what are the two ways to combine resistors

either in a parallel or series fashion

what can we infer about potential difference and current for resistors in a series

potential difference between points is the same no matter which way you go around the circuit, and you can find the total by adding the individual components

current is the same throughout

are these resistors in a series or parallel

series!!!! (all run through same connection to the battery)

is this resistor in a series or parallel fashion

parallel (notice how they each have an individual connection to the battery)

what can we infer about potential difference and current for resistors in a parallel fashion

voltage or potential difference is the same between individual points and the total

circuit between the points is not the same as the total, and the total can be found by adding the individual components

how do you find total resistance of resistors in a series

how do you find resistance for resistors in a parallel fashion

which experiences a lower resistance: resistors in a series or parallel fashion

parallel