Current-Voltage Characteristics

What is a simple electrical circuit require?

• a conductor through which current can flow

• a source of potential difference

What is electric current?

The rate of flow of electric charge

What are the units of current?

Amperes(A) or Amps(A)

What is one amp equal to?

• 1 amp is equivalent to a charge of 1 coulomb flowing in 1 second, or 1 A = 1 C s⁻¹

What is the equation for current

Current = amount of charge flowing(C)/time intervals

When can current flow?

• Current flows when a circuit is formed

  • This is when a conductor, such as a wire, connects two oppositely charged terminals of a source, such as a cell

What is conventional current and how does it flow?

• Conventional current is defined as the flow of positive charge

  • This is from the positive terminal of a cell to the negative terminal

How do electrons really flow?

• Electrons are negatively charged so they flow from the negative terminal of a cell to the positive terminal

This is the opposite of the direction of electron flow

How is current measured?

Ammeter

How is an ammeter connected?

In series with the component measured

What is potential difference in terms of work?

The electrical work done per unit charge flowing between two points

What are the units for potential difference?

Volts(V)

What is 1V equivalent to?

• 1 volt is equivalent to the transfer of 1 joule of electrical energy by 1 coulomb of charge, or 1 V = 1 J C⁻¹

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What is the equation for potential difference?

Potential difference = work done/Charge flow

V = W/Q

What does a simple cell create?

A simple cell creates a potential difference through the separation of charge

How does a simple cell work?

• One end (terminal) of the cell has an excess of positive charge and the other an excess of negative charge

• Negatively charged electrons are repelled by the negative terminal and attracted to the positive terminal

• Therefore, when a wire is connected between the two terminals, the potential difference causes the flow of electrons (current)

How is potential difference measured?

Voltmeter

How are Voltmeters measured?

Voltmeters must be set up in parallel with the component being measured

What is resistance?

The opposition of a component to the flow of electric current through it

What is the resistance of a conductor?

the ratio of the potential difference V across to the current I in it

What is the equation of resistance?

R = V/I

• Where:

  • R = resistance of a conductor (Ω)

  • V = potential difference across the conductor (V)

  • I = current in the conductor (A)

What are the units of resistance?

ohms (Ω)

What is 1 ohm equivalent to?

• A resistance of 1 Ω is equivalent to a potential difference across a component of 1 V which produces a current of 1 A through it

What does the resistance of a component affect?

The current in a circuit

What happens when reistance increases across a given component?

The lower current can flow

What happens when reistance decreases across a given component?

the higher the current that can flow

What is an example of a good conductor and why is it a good conductor?

Copper as it has low electrical resistance

What does Ohm’s law state?

For a conductor at a constant temperature, the current through it is proportional to the potential difference across it

What does a constant temperature imply?

• Constant temperature implies constant resistance

What is the equation for Ohm’s Law?

Potential difference = Current x resistance

V = IR

What is the IV graph for a resistor?

Graph

What is the IV graph of semiconductor diode?

Graphs

What is the IV graph of filament lamp?

Graph

What is the relationship between current and potential differenec in a Ohmic conductor?

• The current is directly proportional to the potential difference

• This is demonstrated by the straight-line graph through the origin

What is a diode?

A component that allows current to flow in one direction

How does the graph of a semiconductor diode look like?

• When the current is in the direction of the arrowhead symbol, this is forward bias. This is shown by the sharp increase in potential difference and current on the right side of the graph

What happens when a diode is switched around?

• When the diode is switched around, it does not conduct and is called reverse bias. This is shown by a zero reading of current or potential difference on the left side of the graph

What doe sthe IV graph of a filament show?

• The I–V graph for a filament lamp shows the current increasing at a proportionally slower rate than the potential difference

What are reasons for trends in the IV graph of a filament graph?

• As the current increases, the temperature of the filament in the lamp increases

• Since the filament is a metal, the higher temperature causes an increase in resistance

• Resistance opposes the current, causing the current to increase at a slower rate
  

What happens as current increases in a filament lamp?

• As the current increases, the temperature of the filament in the lamp increases

• Since the filament is a metal, the higher temperature causes an increase in resistance

• Resistance opposes the current, causing the current to increase at a slower rate