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Resistance and V=IR

• Potential Difference (V) = current (A) X resistance (Ω)
• Practical: investigating the factors affecting resistance
• Ammeter = measures the current flowing through the wire. It must be always placed in series

voltmeter = measures the potential difference across the wire. Must be placed parallel around whatever you are investigating.

1. Attach a crocodile clip to wire level with 0cm on the ruler

2. Attach second crocodile clip to the wire (10 cm away). Note the length of wire in between the clips.

3. Close switch = record current and potential difference through the wire

4. Open switch = move second crocodile clip (another 10cm) = close switch = record new length, current and potential difference.

5. Repeat for different lengths of wire

6. Using measurements of current and potential difference, use R = V/I calculate resistance

7. Plot a graph of length wire against resistance. Draw a line of best fit

8. Graph should be a straight line through origin = resistance is directly proportional to length. Longer wire = greater resistance

9. If doesn’t go through origin = systematic errors.

• Thin wires are best, and wire may heat up which affects resistance, therefore let it cool between readings by opening switch.

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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