12.1 - current and charge

what is needed for an electric current to pass round a circuit?

• the circuit must be complete

• must be a source of potential difference, such as from a battery of cell

what is a source of potential difference in a circuit?

battery or cell

can an electric current pass in an incomplete circuit?

no, the circuit must be complete (closed)

what does a source of potential difference do?

make electric current pass round a circuit

what is the electric current (I)?

the rate of flow of flow of charge in the wire or component

what is the rate of flow of charge in the wire or component?

the electric current

is the electric current any different from the current?

nah

what is the current due to?

the passage of charged particles called charge carriers

what is the passage of charge carriers known as?

current

what are charge carriers?

charged particles passing through a circuit

what are the charge carriers in metal?

conduction / delocalised electrons that move inside the metal, repeatedly colliding with each other and the fixed positive ions in the metal

how do conduction electrons (in metal) carry charge?

since they are delocalised, i.e., free to move, they carry charge by repeatedly colliding with each other and the fixed positive ions in the metal

what do conduction electrons collide with in the metal?

each other, and the fixed positive ions in the metal

what particles are inside a metal?

• delocalised / conduction electrons

• fixed positive ions in the metal

what charged are the fixed ions in a metal?

positive

are the positive ions in the metal fixed or free to move?

fixed

what type of ions are the fixed ions in a metal?

positively charged ions, meaning they have less electrons than protons

what happens when charge is carried through metal?

the conduction electrons repeatedly collide with each other and the fixed positive ions in the metal

what is the charge carrier in a salt solution?

ions (charged atoms / molecules)

how is charge carried through a salt solution?

by the ions (charged atoms / molecules)

what are ions?

charged atoms / molecules, that are charged when an electron is lost or gained in ionisation, causing an unequal number of electrons and protons within the particle

test for conduction of electricity

what equipment is present in a simple test for conduction of electricity?

• test material

• metal clips connecting the test material to the wire

• ammeter

• cell

here

how does a simple test for conduction of electricity works?

• when a conducting material is connected to the circuit, the ammeter shows a non-zero reading as the battery forces the charge carriers through the material to pass through the battery and ammeter

• when a non-conducting material is connected to the circuit, the ammeter will show a zero reading as there are no charge carriers within the material to carry charge across the material, and therefore none to pass through the meter and battery

in a simple test for conduction of electricity, what happens when the material is conducting?

the ammeter shows a non-zero reading as the battery forces the charge carriers through the material to pass through the battery and ammeter

in a simple test for conduction of electricity, what happens when the material is non-conducting?

the ammeter will show a zero reading as there are no charge carriers within the material to carry charge across the material, and therefore none to pass through the meter and battery

in a simple test for conduction of electricity, why does the ammeter show a non-zero reading when the material is conducting?

the charge carriers in the conducting material carry the charge from the current across and back into the wire, connecting the circuit. these charge carriers then can pass through the ammeter on the other side of the material, meaning a non-zero reading is shown

in a simple test for conduction of electricity, why does the ammeter show a zero reading when the material is non-conducting?

there are no charge carriers within the material, therefore the charge in the current cannot pass through the material. since the test material is part of the circuit, if charge cannot pass the material it therefore cannot pass through the ammeter on the other side of the material, meaning a zero reading is shown

how do we test if a material is conducting (of electricity)?

use a simple test for conduction of electricity. if the ammeter has a non-zero reading, the material is conducting as charge carriers can pass through the material, consequently passing through the ammeter and producing a reading

here

how do we test if a material is non-conducting (of electricity)?

use a simple test for conduction of electricity. if the ammeter has a zero reading, then the material is non-conducting as no charge carriers can pass through the material and therefore no charge carriers are passing through the ammeter

here

what is the ammeter for in a simple test for conduction of electricity?

to measure the current after the test material, which will prove the electric conductivity of the test material as charge carriers must be able to pass through the material for the ammeter to have a reading

what is the battery for in a simple test for conduction of electricity?

to provide a source of potential difference across the circuit, allowing current to flow and therefore determining the conductivity of the test material by seeing whether current flows through the material or not

what are the metal clips for in a simple test for conduction of electricity?

to connect the test material to the circuit, so charge carriers will have to pass through the test material and it can therefore be determined whether the material is conducting or not

if the current is passing through a conducting metal, what are the charge carriers across the circuit?

electrons, from the delocalised electrons that are the charge carriers in the metal

if the current is passing through a salt solution, what are the charge carriers across the whole circuit?

ions

if the current is passing through a conducting metal, how much of the circuit has charge carriers of electrons?

all of it

if the current is passing through a salt solution, how much of the circuit has charge carriers of ions?

all of it

what does the type of charge carrier across the circuit depend on?

the conducting material the circuit is passing through -

• if it’s passing through a conducting metal, then all charge carriers across the circuit will be delocalised electrons

• if it’s passing through a salt solution, then all charge carriers across the circuit will be ions

how do electrons flow in a conventional current?

enter the battery at the positive terminal and exit at the negative terminal

how do the electrons flow in actual current?

enter the battery at the negative terminal and exit at the positive terminal

conventional current vs actual current

conventional current: + to -

actual current: - to +

what is the unit for current (I)?

ampere (A)

what is an ampere?

the magnetic force between 2 parallel wires when they carry the same current

what is the magnetic force between 2 parallel wires when they carry the same current?

an ampere

which kind of force is an ampere defined as?

the magnetic force

what is the magnetic force between in the definition of an ampere?

2 parallel wires when they carry the same current

what is the requirement of the 2 parallel lines the magnetic force is between in the definition of an ampere?

they carry the same current

what is the unit for charge (Q)?

coulomb (C)

what is a coulomb?

the charge flow in one second when the current is one ampere, I = Q / t

what is amount of charge flow in the definition of 1 coulomb?

1 second of charge flow

what is the current in the definition of 1 coulomb?

1 ampere

equation linking charge, current, and time

change in charge flow = current x change in time

what is the magnitude of charge of an electron?

1.6 × 10^-19C

how many electrons are passing through a 1A current per sec? how do you prove this?

6.25 × 10¹⁸

WHY???!!!

in electrical terms, how can materials be classified?

• conductors

• semiconductors

• insulators

how does a metallic conductor work?

in a metallic conductor, there are fixed positive ions and delocalised electrons, which are the charge carriers. when a voltage is applied across the metal, the conduction electrons are attracted to the metal’s positive terminal (actual current)

what is the composition of a metallic conductor?

most electrons are attached to atoms but some are delocalised (the charge carriers)

are all particles fixed in a metallic conductor?

what do you think. clue’s in the word ‘conductor’ you dumbass

are all particles delocalised in a metallic conductor?

in fact, no! some are fixed and the delocalised ones are the charge carriers

how does a semiconductor work?

there are delocalised electrons, fixed positive ions, and delocalised electrons locked in atomic bonds. as the temperature increases, the atomic bonds are broken and the number of mobile charge carriers increase

what particles are in a semiconductor?

• delocalised electrons

• fixed positive ions

• delocalised electrons locked in atomic bonds

what increases the conductivity of a semiconductor?

the temperature

why does conductivity in a semiconductor increase with increasing temperature?

the atomic bonds locking the delocalised electrons are broken, and there are more mobile charge carriers

what happens to the resistance in a semiconductor?

it decreases with increasing temperature

why does resistance in a semi conductor decrease with increasing temperature?

TURD ! temperature up, residence down

explain exactly why

what happens in a semiconductor when temperature is increased?

• amount of mobile charge carries

• therefore conductivity

• resistance

what is a pure semiconducting material known as?

an intrinsic semiconductor

what is an intrinsic semiconductor?

a pure semiconducting material whose conduction is due to electrons that break free from the atoms of the semiconductor

what is the conduction in an intrinsic semiconductor due to?

electrons that break free from the atoms of the semiconductor

for the conduction of an intrinsic semiconductor, where do the electrons break free from?

the atoms of the semiconductor

which conducting material’s conduction is due to a electrons breaking free from the atoms of the material?

an intrinsic semiconductor

what is the composition of an insulator?

each electron is attached to an atom and cannot break free

why can’t an insulator conduct electricity?

each electron is attached to an atom, meaning there are no mobile electrons to carry the charge across the material when a voltage is applied

what happens when a voltage is applied across an insulator?

no current passes through the insulator because no electrons can move through the insulator

what kinda battery is a car battery?

a 12V rechargeable battery designed to supply a very large current to start the engine

what is the potential difference of a car battery?

12V

why do car batteries have such a high potential difference?

to supply a very large current to start the engine

is a car battery a disposable or rechargeable battery?

rechargeable

when does the battery in a car recharge?

when the engine is running

what enables a car’s engine to start running?

a large current supplied by a 12V rechargeable battery

what happens to the car’s battery when the engine is running?

it recharges

what are rechargeable batteries used in?

• cars

• portable electronic equipment, e.g., mobile phones

what determines the amount of current a rechargeable battery supplies?

the size of the rechargeable battery

do mobile phones use rechargeable or disposable batteries?

small rechargeable batteries

do mobile phones use large or small rechargeable batteries?

small

which supplies a larger current - a large or small rechargeable battery?

large rechargeable battery

which supplies a smaller current - a large or small rechargeable battery?

small rechargeable battery

which battery is more environmentally friendly? why?

rechargeable batteries, because once disposable batteries are done they are no longer of use and must be thrown away

how is the human genome mapped?

• fragments of dna (carrying a negative charge) tagged with amino acid bases

• voltage applied across strip of gel with spot of liquid containing tagged fragments

• negatively charged tagged fragments attracted to the positive electrode

• fragments separate according to size when moving to the positive electrode

• fragments fluoresce when passing through spot of laser light due to dye attached to each tag

• light sensors linked to computer detect glow from each tag, which then displays the sequence of bases in the dna fragments

in human genome mapping, what is tagged with amino acid bases?

fragments of dna

in human genome mapping, what are fragments of dna tagged with?

amino acid bases

in human genome coding, do the tagged dna fragments carry a charge?

yes, a negative charge

in human genome coding, what charge do the tagged dna fragments carry?

negative charge

in human genome coding, where are the tagged fragments placed?

inside a spot of liquid on a strip of gel that has a voltage applied across it

in human genome coding, what happens to the strip of gel the tagged dna fragments (inside the spot of liquid) are on?

a voltage is applied across it, making the negatively charged fragments attracted towards the positive cathode and move towards it

in human genome coding, what does the voltage do?

make the negatively charged tagged fragments attracted towards the positive cathode and move towards it

in human genome coding, what makes the tagged dna fragments move?

the voltage applied across the strip of gel the liquid spot they’re in is placed upon

in human genome coding, what is the tagged dna fragments attracted to?

the positive electrode

in human genome coding, why are the tagged dna fragments attracted to the positive electrode?

because the tagged dna fragments are negatively charged, and opposite charges attract

in human genome coding, how are tagged dna fragments separated?

by size