Circuit Devices


  • LDR(Light Dependent Resistor) = dependent on intensity of light
  • Bright light = resistance falls
  • Darkness = resistance increases
  • Used in automatic night lights and burglar detectors
  • Thermistor = temp dependent resistor
  • Hot conditions = resistance drops
  • Cool conditions = resistance rises
  • Used in temp detectors (electronic thermostats)
  • Sensing circuits = used toturn on / increase the power to components depending on conditions
  • If components connected in parallel = same potential difference
  • Sensing circuit to control a fan (a thermistor, fixed resistor which is in parallel with the fan)
  • Fixed resistor and fan = same potential difference = connected inparallel
  • The potential difference of the power supply is shared out between the thermistor and the fixed resistor and fan loop = bigger resistance of component = more potential difference it takes
  • As room gets hotter = resistance of thermistor decreases = takes smaller share of potential difference = potential difference across fixed resistor and fan increases = fan goes faster

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……?’








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

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