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1. ### Foca length of a concave mirror

Well any more hints? I can't think of any equation finding new f using angles.
2. ### Foca length of a concave mirror

Homework Statement A concave mirror of focal length 10cm in air is put into a beaker containing a liquid up to 7.5cm. Refractive index of the liquid is 1.2. What is the focal length of the mirror inside the beaker? The Attempt at a Solution I tried proportion method: Depth...
3. ### Finding New Resistance

I struggle with A = π r^2 and you cleared those. Thanks a lot.
4. ### Finding New Resistance

I'm sorry but according to your equation, I don't get the answer which is 1.18cm. By the way, I also don't understand the statement "carbon film on its curve surface" means. Do you mind explaining it?
5. ### Finding New Resistance

I got it. I thought the increase of L decrease the r to r/1.1. Can I ask another question about resistance? A square carbon film of thickness 5x10^-7m, rho 4x10^-5 ohm m is formed on an insulator rod of diameter 3mm.What is the length of the rod so that the carbon film on its curve surface has...
6. ### Finding New Resistance

R=rho*l / A I just don't get the part how the length of the wire affects the cross sectional area/radius.
7. ### Finding New Resistance

A wire has uniform cross sectional and resistance R. Then the wire is pulled so that the length increases by 10%. How to find the new resistance? Assumption: The wire thins uniformly.
8. ### Question about Electric Field Strength and Electric Potential

Lets say I have a point charge X placed on a region between a +Q test charge and +2Q point charge where electric field strength is zero. Since E=-dV/dR, does it mean V=0 or constant? Can the point charge move if i place it there? Well lets just ignore gravitational field/force here.