Ohms%Law%%

BTEC%%

Key terms

•  Current is the flow of electrons around a circuit.

•  Voltage is the driving force that pushes the current around.

•  Resistance is anything in the circuit that slows down the flow.

•  Voltage pushes and the resistance is opposing it, together they decide what the current will be.

What%is%Ohms%Law?%

•  Ohm's Law describes the relationship between voltage, current and resistance in a simple electrical circuit.

•  The law is named after early 19th century German physicist, George S Ohm.

Georg Ohm (1789-1854), a German Physicist.%

Ohms%law%

•  Ohm%found%that%the%current%in%a%circuit%is%directly%propor<onal%to%the%voltage%and%inversely%propor<onal%to%the%resistance%in%the%circuit.%%

%Can%you%think%of%an%equa<on%that%relates%to%all%3?%

Think%about%their%symbols%%%

Ohms%law.%

The%three%truths%in%Ohm's%Law%are:%%•  if%resistance%remains%the%same,%the%current%flow%goes%up%or%down%if%voltage%goes%up%or%down%%

•  when%resistance%goes%up,%the%current%goes%down%so%long%as%the%voltage%remains%the%same%%

•  and%when%resistance%goes%down,%current%goes%up%if%the%voltage%is%s<ll%the%same.%%

Fill%the%gaps%%

The%three%truths%in%Ohm's%Law%are:%%•  if%__________remains%the%same,%the%current%flow%goes%up%or%down%if%voltage%_______or%down%%

•  when%resistance%goes%up,%the%_________down%so%long%as%the%voltage%___________%the%same%%

•  and%when%resistance%goes%down,%current%goes%up%if%the%________________.%%

Key terms

•  Current is the flow of electrons around a circuit.

•  Voltage is the driving force that pushes the current around.

•  Resistance is anything in the circuit that slows down the flow.

•  Voltage pushes and the resistance is opposing it, together they decide what the current will be.

Crea<vity%%

Senario you have been selected to explain the relationship between V I &R to a class of year 5 students who are visiting STS for the afternoon.

How could you show what is happening inside the wires with resistance?

Be creative.!!!

Measured in Volts (V).

Measured in Ohms(Ω). Measured in Amps (A).

V#

A#Ω#

V = I x R

P = V x I

V = I x R

I = V ÷ R

Power is the amount of energy consumed or released by a circuit. Power can easily be found if you know the voltage and the current.

Calcula<ons%%

•  Calculate%the%voltage%in%a%circuit%when%the%current%is%5.4%amps%and%the%resistance%is%6%Ohms.%

•  Calculate%the%resistance%when%The%voltage%is%12%volts%and%the%current%is%5%amps.%

A#

V%

Variable Resistor

Ammeter

Voltmeter

Bulb

Cell

Voltage (V) volts Current (I) Amps Resistance (R) ohms

Use the table below to record your results. Draw a sketch of your circuit below

• How%should%a%voltmeter%be%connected%in%a%circuit?%%%%

•  An%Ammeter?%%%%%%%%%%%%%%%%%%%%%%%%%%%Grade%C%

• What%is%another%name%for%Voltage?%%%%%%%(Grade%C)%

•  Draw%a%simple%circuit%that%contains%a%cell%a%bulb%an%ammeter%and%a%voltmeter.%%%%%(Grade%C)%

• What%was%the%man’s%name%that%discovered%the%rela<on%ship%between%VI&R.%%%%%%

(for%fun)%

•  Calculate%%the%current%when%the%voltage%is%6%v%and%the%resistance%3.2%ohms.%

•  Show%all%working.%

(B)%%

•  Calculate%the%power%(P)%%%%%%%%%%%%%%%%%%%%%%%%%%%of%the%circuit%when%the%voltage%is%240V%and%the%current%is%14amps.%

•  (Grade%A)%

Circuit Symbols

%b% M%#%b%

Power Supply Open Switch Closed Switch

Fixed resistor Variable resistor Diode%%

LED LDR Motor

Thermistor Fuse Heater