Circuit, current and poetantial difference

What happens to the current as the resistance changes? (in a given p.d )

The greater the resistance of a component the smaller the current for a given potential difference.

The relationship between voltage and resistance while current stays constant

The current through the ohmic conductor (at a constant temperature) is directly proportional to the potential different across the resistor.

meaning the resistance remains constant as the current changes.

(directly proportional straight line graph)

The resistance through a filament lamp and how would the graph look.
(what factors affect the filament lamp and its resistance, other than va)

The resistance of a filament lamp increases as the temperature of the filament increases.

(the squiggly graph {similar to rates} which goes both ways)

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The resistance through a diode and how would the graph look.

The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.

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(the graph starts and goes up only on the right side)

From where does the current flow in a circuit and why?

Goes from the positive terminal to the negative terminal

Electrons are **negatively charged**

* Therefore, they flow **away** from the positive terminal of a cell **toward** the negative terminal

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In a battery or cell, the positive side is the longer end

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* Conventional current is defined as the flow of **positive** charge from the **positive terminal of a cell to the negative terminal**
* This is **opposite** to the direction of electron flow, this is because the conventional current was being put to use before the discovery of the electron

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Why does all the component in a closed-loop (series) circuit have the same current everywhere?

Because the number of electrons per seconds that passes through one part of the circuit is the same number that passes through any other part.

Do good conductors and insulators have high or low resistance and why

• Resistance is defined as the opposition to current:

  • The higher the resistance of a circuit, the lower the current

  • This means that good conductors have a low resistance

  • insulators have a high resistance

How to avoid systematic errors in the investigation of resistance using lengths of wire

* The first crocodile clip (connected to the circuit, not the wire) must start at 0 on the ruler
* Otherwise, this could cause a **zero error** in your measurements of the length

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* Both the ammeter and voltmeter should be checked to start from 0

How to avoid random errors in the investigation of resistance using lengths of wire

• Only allow small currents to flow through the wire

  • This keeps the temperature of the wire constant, so it doesn't change its resistance

• The current should be switched off between readings so its temperature doesn't change its resistance

• Add more resistors in series and parallel to calculate the effect on the combined resistance

safety considerations in an investigation of resistance using lengths of wire

* When there is a high current flowing through a thin wire, the wire will become very hot
* Make sure never to touch the wire directly when the circuit is switched on

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* Switch off the power supply right away if burning is smelled
* Make sure there are no liquids close to the equipment, as this could damage the electrical equipment if spilled

What happens to the resistance of a circuit as temperature increases? which components are affected by the temperature?

thermistors and filament lamps.

* All solids are made up of vibrating atoms
* The higher the temperature, the faster these atoms vibrate

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* Electric current is the flow of free electrons in a material
* The electrons collide with the vibrating atoms which impedes their flow, hence the current **decreases**

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* So, if the current decreases, then the resistance will increase (from *V = IR*)
* Therefore, an increase in **temperature** causes an increase in **resistance**

the relationship between the resistance of an LDR and light intensity

As the light intensity **increases** the resistance of an LDR **decreases** and vice versa

random errors in an investigation of IV chrachteristics

* the voltmeter and ammeter will still have some resistance, therefore the voltages and currents displayed may be slightly inaccurate
* The temperature of the equipment could affect its resistance. This must be controlled carefully
* Taking multiple readings of the current for each component will provide a more accurate result and reduce uncertainties

Charachteristics of series circuit

• there is the same current through each component

• the total potential difference of the power supply is shared between the components

• the total resistance of two components is the sum of the resistance of each component.

charachteristics of a parallel circuit

• the potential difference across each component is the same

• the total current through the whole circuit is the sum of the currents through the separate components

• the total resistance of two resistors is less than the resistance of the smallest individual resistor.

How to dind the resistance from the graph?

R= 1/gradient

* Use one fixed resistor **OR** 100 Ω / 200 Ω / 400 Ω / 500 Ω resistor; \[1 mark\]
* Vary the potential difference across the component using the variable resistor; \[1 mark\]
* For each value of potential difference, record the reading of current; \[1 mark\]
* Take repeat readings and calculate a mean; \[1 mark\]
* Turn off the power supply between measurements to prevent the wires from heating (as this will cause a confounding variable because temperature affects resistance); \[1 mark\]
* **Reverse the terminals of the power supply to repeat at negative values of potential difference; [1 mark]**

In any practicals regarding measuring resistance

Reverse the terminals of the power supply to repeat at negative values of potential difference;

Disadvantages of connecting multiple lamps in series?

• If one goes out then the other one also goes out'

• the lamps would be dimmer

In the exam, if it refers to calculating something for any (house hold) appliences what values should you use?

230 v