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Optics question

Hello,I dont know how to do this short exercise,I mean it does not make any sense.The only thing i know  is that the answer is 3.3cm  but i cant do the procudure finding the same result.This is the exercise:
A concave mirror makes a 3 cm image of a 6 cm object when the object is placed 10 cm from the mirror. What is the focal length of the mirror?

It really would help me if you lend me a hand on this.
many thanks

Daniel posted

Answer

15496257000686727171130204739555.jpg

Maxwell’s equations for electromagnetic waves

Physicists illustrate EM waves as perpendicular E and M waves. That seems consistent. What does not make sense is the illustrations showing the E wave phase equal to the M wave. This seems to violate Maxwell’s equations.
The largest E potential would seem to be when the M wave is at a maximum of di/dt when the M wave crosses the zero axis. When maximum changes to the E wave magnitude occur as the E wave magnitude crosses the 0 axis then would not this correspond to the maximum in the M wave?
The wave nature of electromagnetic waves, as a consequence of Maxwell’s equations, makes sense except it would appear that the E and M waves should have a 90 degree separation. What am I missing?

John Varga asked

The following links may help you

http://physics.bu.edu/~duffy/PY106/EMWaves.html

Electromagnetic Waves and their Properties

http://farside.ph.utexas.edu/teaching/302l/lectures/node119.html

A Physicist Driver confusing Police

A driver is stopped for running a red light. trying to avoid a ticket, the driver tells the police officer that because of the Doppler shift, the red light (650 nm) was blueshifted to a green light (470 nm). what would the drivers speed need to be for this to be true

 

Asked Sabnna

Would an underground nuclear explosion generate an Electromagnetic pulse?

Would an underground nuclear explosion generate an EMP? If so, how far would it be likely to travel?

Asked Daniel

You can get answer to your question here. If you need further clarification, please post as comment to this post.\

https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse

http://www.futurescience.com/emp.html

The indigenous Cryogenic Engine of India

The cryogenic engine used in indian rocket gslv is also called as?

Asked Shaaru

Answer: CE 7.5 was the first successful engine and CE-20 is the Cryogenic Engine developed by the Liquid Propulsion Systems Centre, a subsidiary unit of ISRO developed to power the upper stage of the Geosynchronous Satellite Launch Vehicle MK III  also referred to as the Launch Vehicle Mark 3 (LVM3).  It is the first Indian cryogenic engine to feature a gas-generator cycle   References ISRO website https://www.isro.gov.in/gslv-d5-gsat-14/indigenous-cryogenic-engine-and-stage    

Siphons and fluid dynamics

Working on a science fair project with my 3rd grader we got an unexpected result I am at a loss to explain.  We made a mock up toilet with two different drain pipes / siphons.  When we use the 3/4″ pipe we get a slow drainage that stops when the water in the bowl goes down to about the level of the crest of the siphon.  When we use the 1 1/2″ drain pipe we get a very strong flow and the water level drops all the way down until air can enter the siphon, so the water level drops way below the top of the siphon, down to the intake opening.  I understand that more water travels though the larger pipe, hence the faster flow rate, but I can’t explain the difference in the ending water level in the bowl.  What forces are at work here?  How can we further test or prove these principals?

 

Asked Dan

Why do we take differential element “dx” from the origin at a distance “x” only?

Why do we take differential element “dx” from the origin at a distance “x” only.(the variable “x” and x in “dx” are same.why?)

 

Asked Suraj

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