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Resistance and I-V Characteristics

• For some components: as current through them is changed = resistance of component changes
• Resistance of ohmic conductors (wire or resistor) = DOESN’T change with current. At constant temperature = current flowing is directly proportional to potential difference across it.
• Resistance of some resistors and components DOES change (diode or filament lamp)
• Electric charge flows through a filament lamp  transfers some energy to thermal energy store  designed to heat up. Resistance increases with temperature = as current increases = filament lamp heats up more = resistance increases
• Diodes = resistance depends on the direction of current. They let current flow in one direction, but in the other direction there is avery high resistance .
• PRACTICAL: I-V Characteristics
• I-V Characteristic = a graph which shows how current flowing through a component changes as potential difference is increased.
• Linear components = I-V characteristic is a straight line = fixed resistor
• Non – linear components = I-V characteristic is curved = filament lamp and diode
• 1. Set up test circuit (a cell, variable resistor, component with a voltmeter around it and an ammeter)

2. Vary the variable resistor = alters the current flowing through the circuit and potential difference across the component

3. Take lots of readings from the voltmeter and ammeter. Repeat reading to get averages

4. Swap over the wires which are connected to the cell = direction of current is reversed

5. Plot a graph of current against voltage

• Ohmic conductors = current (at constant temp) is directly proportional to voltage = straight line
• Filament lamps = as current increases, temp of the filament increases, so resistance increases . So less current can flow = curve
• Diode = current only flows through one direction . Diodes have a high resistance in the reverse direction.

How long have you…? (present perfect 4) Exercises

Use the information given to create questions beginning with ‘How long…?’

• It is snowing.

• The weather is shining.

• John and Kate are married.

• My brother has gone on holiday.

• My aunty and uncle live in Canada.

• My sister is a teacher.

• I work at the chemist.

• I’ve known Susan since I was a baby.

• Jonathan is learning to speak to Mandarin.

Fill in the missing gaps in the sentences using the present perfect (=has/have + past participle)

• I have known Kate a long time.

• My brother has been playing the piano he was 11 years old.

• My mum and dad on holiday to America. They

gone since last Sunday.

• I Ben and Emma since primary school.

We to the same primary and secondary school.

• My sister learning to speak French because she
is going to France next month.

Use the appropriate words in the missing gaps.

have you lived       lives      to

has been       works        have known

I have bought       have worked.

• My sister in Spain. She is studying Spanish

with her friend Rosie. I Rosie since I was 5.

• Spencer like with Jamie. They have worked

together for 2 years.

• How long in Australia?

• a new dress for prom.

• He to Thorpe park.

Challenge: Create 4 of your own questions beginning with ‘How long……?’

1.

2.

3.

4.

1 2 3 4 5 6

“Every accomplishment starts
With the decision to try.” Gail Dever

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