Physics 9

Static & Electric Charge, Voltage, Circuits & Current, Resistance & Ohm's Law

What is static charge?

electrical charge that can be held in one place (static electricity)

How does static charge build up?

2 insulators rub together = friction → e- transferred through materials… now 1+ and 1-

What is an insulator material?

does not allow charges to move easily. ex: when one end becomes + the other will stay the same

What are examples of insulators?

glass, dry wood, ceramics, plastic, rubber

What is a conductor material?

allows electrons to travel freely.

Why are metals good conductors?

metal atoms have at least 1 valence e- that can transfer.

What material can retain static electricity?

Only insulators since it is held in one place

What are the properties of static charge?

never created/destroyed and charging = moving charge to different places

What is the unit of measurement for electrical charge?

Coulomb (C)

What is an electroscope?

detects static charge

What is a danger precaution about static charge?

Grounding = charge → Earth’s surface

What is a contact force?

apply force only on objects they touch (push/pull)

What are forces that act at a distance?

apply force without touching. Ex: gravitational, magnetic, electric force

What is an electric force?

a push or pull between charged objects

What are the laws of electric force?

1\. Opposites attract

2\. Same repel

3\. Neutral is attracted to charged

What happens to the force if you increase the charge?

it is stronger

What happens to the force if the distance of charged increases?

it is weaker

What is Induction?

transferring electrons with no physical contact

What is conduction?

transferring electrons with physical contact

What is static discharge?

Static charge will dissipate, move into air moisture or spark

What is electric current?

electric charge moving though a wire

What is another name for voltage?

potential difference

What is voltage?

a measure in the difference of energy between two points

How and what is voltage measured in?

Voltmeter (outside circuit) and in volts (V)

When charges/electrons pass through a cell they…

gain potential energy (or the potential to do something)

What does an electrochemical cell do?

Converts chemical energy to electrical energy and gives electrons stored potential energy

What are the types of electrochemical cells?

Dry (flashlights) and wet (car)

What are the terminals?

electrodes = metal → anode (-) or cathode (+)

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What is the paste/liquid solution in a cell called?

electrolyte

How does a battery produce voltage?

chemical reaction → charges separate in electrolyte but charges attract so it takes energy to pull apart = chemical →electrical energy = the potential for the electrons to move

What is energy and work and its unit?

energy is the ability to do work, work measures the transfer of energy, unit Joules (J)

What is an electrical current?

flow of electrons past a certain point within a time frame

What is current measured in and with what?

Ammeter (in series) ampres→amps (A)

If there is more electrons what is the current?

It is bigger

Does the current change within a circuit?

No

What are the circuit components?

1. source of electrical energy (cell/battery)
2. Conductor (wire)
3. Switch
4. Load = electrical energy →other forms of energy

What is resistance?

a measure of how much a material tries to stop electricity passing through it

How is there resistance?

electrons collide with metal atoms = vibration → heat

What is a resistor?

reduces current, (also use: transfer electrical energy to heat and light energy)

What affects resistance?

1. material
2. length
3. temperature - decrease = decrease in resistance
4. thickness - increase = increase in surface area → decreases collisions

What is the relationship between voltage and current?

Voltage increases = current increases

What is the relationship between resistance and current?

resistance decreases = current increases

What is Ohm’s Law?

Voltage = Current x Resistance

What is Ohm’s Law measured with and unit?

Ohmmeter, ohm (Lululemon symbol)

When there is a k before the unit… but when there is an m…

multiple by 1000…divide by 1000

What is a series circuit?

only one pathway for electricity to flow (no branches)

What is a parallel circuit?

more than 1 loop (multiple branches)

What is the formula for voltage in a series circuit?

V(source) = V(load 1) + V(load 2) + V(load3) + …

What is voltage in a series circuit?

each load loses a portion of total voltage, voltage across loads add up to total voltage supplied by battery/cell

What is the formula for current in a series circuit?

I(source) = I(1) = I(2) = …

What is current in a series circuit?

current at each part in circuit is equal to total current supplied by battery/cell

What is resistance in a series circuit?

more resistors = more resistance, if total resistance increases total current decreases

How do you find resistance in a question?

Use Ohm’s Law

What is the formula for voltage in a parallel circuit?

V(source) = V(load 1) = V(load 2) = …

What is voltage in a parallel circuit?

voltage is the same throughout circuit and equal to battery

What is the formula for current in a parallel circuit?

I(source) = I(1) + I(2) + I(3) + …

What is current in a parallel circuit?

divided into pathways that will rejoin , current through each pathway adds up to total current in the battery

What is resistance in a parallel circuit?

when resistors are placed in parallel = another pathway so total resistance decreases = current leaving battery increases

What are the 2 types of energy sources?

renewable = naturally replenished

non-renewable = can’t be replaced by natural means quickly enough to keep up with demand

How do generators work?

Fossil fuels → power stations → burnt = heat energy

Heat energy + water = steam

steam + turbines = generators

What are electrical generators?

a device to turn kinetic energy in turbines to electrical energy

How do electrical generators work?

magnet near wire = flow of electrons/electrical charge, electricity generated →cables → National Grid

How does coal create electricity?

1. powdered coal blown into furnace
2. coal burns = water heats in boiler
3. water → high pressure steam
4. steam turns turbine
5. turbine turns shaft connected to generator
6. generator turns = electricty

What is AC?

alternating current is electrical current produced by generators that can change direction. ex charging phone

What is DC?

Direct current is a source of portable electricity, ex. battery

How does DC work?

stores chemical energy that can change into electrical energy but cells might go flat (run out of chemical energy unless rechargeable