# Unit 1: Electricity

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• Unit 1: Electricity
• Current, Amps (I)=Q/T
• Current is rate of flow of charge
• Measured using an Ammeter in series
• Potential Difference, Volts  (V)= W/Q
• Measured using a Voltmeter in Parallel
• Work Done (Joules) per unit charge (Coulomb) to move charge through a resistor.
• Resistance,Ohms          (R) =V/I
• Resistance is a measure of difficulty in the flow of current in a circuit or component
• Ohms Law: As long as temperature is constant; the current through a Ohmic conductor is directly proportional to the potential difference across it
• I/V Charactistics; On a graph a curve shows R is changing and not constant. If the gradient is SHALLOWER then the RESISTANCE IS HIGHER
• Metallic Conductors (Most) are Ohmic therefore have a straight graph
• Filament Lamp has a curve, the metal wire heats up causing more resistance
• Semiconductors; are used in sensors
• Thermistors; different types. Such as (NTC) Negative Temperature Coefficient
• Light Dependent Resistors
• More energy releases, more charge carriers
• Resistivity (?) ?m= (R*A)/L [Resistance x Surface Area (M^2)]/Current
• Superconductors have little/no resistance. This can be forced by cooling a material below its transition temperature
• Can make strong electromagnets that don't need constant power source
• Power, Watts (P)=IV
• Resistance,Ohms          (R) =V/I
• Resistance is a measure of difficulty in the flow of current in a circuit or component
• Ohms Law: As long as temperature is constant; the current through a Ohmic conductor is directly proportional to the potential difference across it
• I/V Charactistics; On a graph a curve shows R is changing and not constant. If the gradient is SHALLOWER then the RESISTANCE IS HIGHER
• Metallic Conductors (Most) are Ohmic therefore have a straight graph
• Filament Lamp has a curve, the metal wire heats up causing more resistance
• Semiconductors; are used in sensors
• Thermistors; different types. Such as (NTC) Negative Temperature Coefficient
• Light Dependent Resistors
• More energy releases, more charge carriers
• By combining Power and Resistance you can say that:
• P=I^2*R
• P=V^2/R
• 1 Watt =1 Joule / Second
• Energy, Joules (J)= P x t
• E=V*I*t
• E=(V^2/R)*t
• E=I^2*R*t
• Energy, Joules (J)= P x t
• E=V*I*t
• E=(V^2/R)*t
• E=I^2*R*t
• EMF and Internal R
• ?= V+v
• ?=IR+ir
• V = ? - v
• V= ? - Ir
• Low IR is great for batteries as less energy is lost. For safety high voltage power supplies have high IR so a short allows only a small current to flow
• Terminal PD is the EMF - lost volts
• V = ? - v