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1. "If an object is illuminated by an extended source (not a point source), the umbral region of the shadow is the area which no light reaches. The penumbral region is the area which is reached by some of the light from the source, but is not fully illuminated.

A strip light of length w=10cm casts a shadow of an opaque object O, which has width 1.0m, onto a screen. The light and object are u=20cm apart and the object and screen are v=50cm apart. What is the width of the umbral region of the shadow? Give your answer to 2 significant figures."

I have a few more questions where something supposedly simple isn't 'clicking'; I will be grateful for any help.
2. (Original post by ombtom)
"If an object is illuminated by an extended source (not a point source), the umbral region of the shadow is the area which no light reaches. The penumbral region is the area which is reached by some of the light from the source, but is not fully illuminated.

A strip light of length w=10cm casts a shadow of an opaque object O, which has width 1.0m, onto a screen. The light and object are u=20cm apart and the object and screen are v=50cm apart. What is the width of the umbral region of the shadow? Give your answer to 2 significant figures."

I have a few more questions where something supposedly simple isn't 'clicking'; I will be grateful for any help.
I would approach this question by drawing a diagram by drawing the light source, object, and the screen. Remember to label the width and distance as well. After this, you will need to draw the shadows properly.

When you have done so, the rest is just trigonometry and similar triangles. Hint: The 2 triangles formed behind the object and adjacent to the umbra has the same angle as the triangle in front of the object.
3. (Original post by hermionegrangcr)
I would approach this question by drawing a diagram by drawing the light source, object, and the screen. Remember to label the width and distance as well. After this, you will need to draw the shadows properly.

When you have done so, the rest is just trigonometry and similar triangles. Hint: The 2 triangles formed behind the object and adjacent to the umbra has the same angle as the triangle in front of the object.
I did it; thank you.

4. (Original post by ombtom)
I did it; thank you.

Quick question, is there any significance to the comment of it not being a point light source? Thank you.
Quick question, is there any significance to the comment of it not being a point light source? Thank you.
Yes; there was a follow up question about that. If it were a point source, there would be no penumbrae.
6. (Original post by ombtom)
Yes; there was a follow up question about that. If it were a point source, there would be no penumbrae.
This better not come up on the PAT
This better not come up on the PAT
At least you know it can't be a 20 mark question this year.
8. (Original post by ombtom)
At least you know it can't be a 20 mark question this year.
Watch how there is a 9 marker on moon phases and eclipses, and I unfortunately need to skip it LOOL. BTW you have any predictions for the topics that might come up? A wave/inteference questions hasn't appeared very often.
Watch how there is a 9 marker on moon phases and eclipses, and I unfortunately need to skip it LOOL. BTW you have any predictions for the topics that might come up? A wave/inteference questions hasn't appeared very often.
The format for the physics section is changing a lot so it's hard to say. The maths sections are quite repetitive so there should be stuff like simple logarithms, ratio of area of shapes, binomial expansion, integration for area, probability, series, and graph sketching. In the physics section, there will probably still be something about circuits (e.g. finding effective resistance), Kepler's 3rd law, KE/GPE transfer, ideal gas law, and simple mechanics. I'm hoping magnetism doesn't come up; it's in the syllabus but I'm not sure what level of knowledge they expect.
10. (Original post by ombtom)
The format for the physics section is changing a lot so it's hard to say. The maths sections are quite repetitive so there should be stuff like simple logarithms, ratio of area of shapes, binomial expansion, integration for area, probability, series, and graph sketching. In the physics section, there will probably still be something about circuits (e.g. finding effective resistance), Kepler's 3rd law, KE/GPE transfer, ideal gas law, and simple mechanics. I'm hoping magnetism doesn't come up; it's in the syllabus but I'm not sure what level of knowledge they expect.
Yeah, pretty much the same stuff for maths. Loads of the geometry and the area/ratio things can be found on the SMC papers which is good practice. I don't think thermionic emission will come up again it was a 6 marker on one of the previous papers. TBH i don't want any of electricity to come up :/ Well, unless its finding effective resistance.

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