2. A quick recap from last lesson
In pairs, take it in turns to explain one of these key terms from last lesson. Ask each other if you are unsure and if you can’t do it individually, work together to come up with an explanation. Refraction Power Dioptre Curvature Focal point Principal axis
LESSON OBJECTIVES: ALL MUST: Take a series of results to compare distances in image formation. MOST SHOULD: Be able to make links between these distances and the power of lenses. SOME COULD: Consider and evaluate the uncertainties involved in the experiment.

3. Chapter 1
The Eye

4. Learning Objectives
To know that a converging lens adds a curvature to light falling on it.
The curvature added is the power of the lens.
To know the lens equation.
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5. Learning Outcomes ALL MUST:
Take a series of results to compare distances in image formation.
MOST SHOULD:
Be able to make links between these distances and the power of lenses.
SOME COULD:
Consider and evaluate the uncertainties involved in the experiment.
Grade E
Grade C
Grade A
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6. Power and Focal Length KEY POINTS SO FAR:
Lenses add curvature, centred around the focal point, so waves can be brought to focus.
The more powerful a lens, the more curvature it adds
Power = 1/f
C = 1/v
Power AND Curvature are both measured in Dioptre
LESSON OBJECTIVES: ALL MUST: Take a series of results to compare distances in image formation. MOST SHOULD: Be able to make links between these distances and the power of lenses. SOME COULD: Consider and evaluate the uncertainties involved in the experiment.

7. Object, Image & Focal Length
u is always considered to be negative as it is “this side” of the lens
Cartesian Sign Convention – the origin is at the centre of the “optical component” ie: the lens!
LESSON OBJECTIVES: ALL MUST: Take a series of results to compare distances in image formation. MOST SHOULD: Be able to make links between these distances and the power of lenses. SOME COULD: Consider and evaluate the uncertainties involved in the experiment.

8. 190E: Investigating converging lenses.
Aim: Determine the relationship between u and v for a converging lens.
Before you start: measure the focal length of your lens using a white piece of card.
Once you have your results......
Plot a graph of 1/u against 1/v and u against v.
We will analyse these together afterwards.
Aim to get 10 sets of results.
u (m)
v (m)
1/u (D)
1/v (D)
Once u=0.1m you will struggle to form an image
LESSON OBJECTIVES: ALL MUST: Take a series of results to compare distances in image formation. MOST SHOULD: Be able to make links between these distances and the power of lenses. SOME COULD: Consider and evaluate the uncertainties involved in the experiment.

9. Reviewing our results…
If you move the bulb closer to the lens, what happened to the distance needed between lens and screen for image to be in focus and vice versa? Why? Can you explain these ideas in terms of curvature? Use diagrams to help you if need be.
LESSON OBJECTIVES: ALL MUST: Take a series of results to compare distances in image formation. MOST SHOULD: Be able to make links between these distances and the power of lenses. SOME COULD: Consider and evaluate the uncertainties involved in the experiment.

10. On a piece of graph paper, using an object height of 3cm and a lens of focal length 4cm.
Draw a lens diagram to show what sort of image is formed when the object is placed at 2F.

11. Getting to Grips with Graphs!
There are 4 graphs. Annotate yours with ONE thing you know from or one statement you can make about the graph you are looking at.

12. Learning Objectives Practise using the lens equations.
Use graphs to find values of known constants.
Review lens diagrams from GCSE.
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13. Learning Outcomes ALL MUST: Practise using the lens equation.
MOST SHOULD:
Be able to use two different graphs to determine an unknown focal length.
SOME COULD:
Apply ideas from ray diagrams to understand the necessary points to use on the graphs.
Grade E
Grade C
Grade A
Thursday, 25 April 2019 18

14. Why isn’t the image formed at the focal point????
The Lens Equation
Overall, the formula relating the curvature of the wavefronts leaving a lens to the curvature of the wavefronts entering it is:
1 = 1 + 1
v: distance between the lens and the in-focus image
u: distance between the lens and the object
f: focal length of the lens
Why isn’t the image formed at the focal point???? v u f
LESSON OBJECTIVES: ALL MUST: Take a series of results to compare distances in image formation. MOST SHOULD: Be able to make links between these distances and the power of lenses. SOME COULD: Consider and evaluate the uncertainties involved in the experiment.

15. Cartesian Sign Convention – the origin is at the centre of the “optical component” ie: the lens!
u is negative...

16. Example
A camera lens with a focal length of 5 cm forms a clear image of an object on a film when the object is 3 m from the lens.  
Will the image be more or less than 5 cm from the lens? Explain your answer.
[Hint: Is the object distance positive or negative?]

17. Using graphs to determine f
1/v v
1/u u

18. QOTD

19. Question 1

20. Question 2
With a zoom lens you can vary the power of a lens. What is the power required to focus a flower that is 250mm in front of the lens on a film that is 50mm behind the lens?

21. Question 3
A lamp 400mm from a lens is in focus on a screen 400mm from the lens on the other side of the lens. What is the power and focal length of the lens?

22. Question 4