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# Practice ISA lesson 1:

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## D. O'Keeffe

on 2 November 2015

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#### Transcript of Practice ISA lesson 1:

What do you know about Light-dependent resistors?
Physics ISA
1) Writing a hypothesis and source comparison

2) Creating a method for investigating your hypothesis (draft and neat)
Equipment
Method
Risk assessment
Control variables
Context

3) Carrying out the investigation and collecting results

4) Interpreting the results
Physics ISA lesson 1:
Hypothesis and Sources

Context: Attenborough building
The school’s leadership want the lights to automatically come on when the natural light becomes too dim.
This is a safety concern, a timer does not take into account variations from day to day!

The desire is for the lights to switch on automatically

For this to happen the SLT have been told that they will need to use a Light Dependent Resistor (LDR)

But they don’t know how to use them!

They can use a automatic switch that is controlled by the LDR

But they can't remember what factors affect the resistance of the LDR…
Take a note of the context in your books if you are confused:
speak up!
As light intensity increases the resistance of an LDR decreases.

When light intensity is high, resistance is low and current can flow (high current)

When light shines on an LDR it releases electrons to carry the current. Thus as the light intensity increases the current increases resulting in a reduction in resistance. In the dark no extra electrons are released so there is greater resistance.

What is a hypothesis?
A prediction about what you expect to happen in your investigation e.g:
The more concentrated an acid is, the quicker it will react with magnesium
So you need to describe what variables you will be investigating for a
LIGHT DEPENDENT RESISTOR
10X1 Hypothesis:
Source comparison