# Gravitational Lensing

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Questions in this category have been asked by PJ, MT and SR

- How can you use gravitational lensing to determine H0?
- What is the deflection of light by sun using newtonian mechanics? (calculate it, do the integral)
- Compare it with the GR result

- What kind of objects can cause gravitational lensing?
- what's the smallest thing we know that causes lensing?

- "Do you know anything about Gravitational Lensing? Write down any equation related to lensing." (SR)
- How do you determine the magnification of a gravitationally lensed image from the lens equation? (SR)

- How would one calculate the deflection angle of light using GR? (SR)
- Write down the lens equation. (SR)
- What is a typical size of an Einstein radius? (RS? SR? I can't remember who asked.)
- In microlensing, how does one detect a lensing event, given that one does not see a clear Einstein ring? (SR,MT)
- How is this effect related to the lensing potential? (SR, MT)

- Write down the lens equation for an isothermal sphere and a point mass. What is the Einstein radius?
- How would you compute the magnification? How would you do this without any equations? (SR)

- What is the cross section for a stellar mass lensing event, a planet sized lensing event? Why do we see planet lensing events? (SR)

- What are the observational difficulties of weak lensing measurements? (MT)

- Why is there a sweet spot for gravitational lenses around redshift .7?
- What is the Newtonian lensing result and how does it differ from the relativistic result?
- Are the D's in the formula for the Einstein radius angular diameter distances, luminosity distances, or comoving distances?