# Plane vs convex vs concave mirror​

• Réponse publiée par: molinamaureen080693

plane mirror - is a flat mirror

convex mirror - is bulging outwards

concave mirror - is bulging inwards

• Réponse publiée par: Rosalesdhan

do rotating magnets create energy? where can i find more information on this subject?

the first law of thermodynamics is that matter/energy cannot be "created" or destroyed. we can convert energy from one form to another. for instance, in a car, we convert chemical energy (actually the binding energy of electrons) to heat, which in turn is converted to kinetic energy (motion).

your question has a similar answer. when you rotate a magnet, you are using kinetic energy to move it. this kinetic energy can be converted to electrical energy by taking advantage of the properties of electromagnetism. since you can't "create" energy, the amount of electrical energy produced will always be the same or less than the amount of energy you put in. actually, it can't be exactly the same, because there is always at least some energy converted to heat by friction. this wasted energy results in an energy conversion "efficiency" which is less than 100%. the classic application of your example is the electric generator.

one of the most useful and beautifully symmetric principles in physics is the connection between electricity and magnetism. this connection can be described like this.  electrons  feel the force exerted by a magnetic field. this is because electrons behave like tiny magnets, with north and south poles. so a magnetic field will have an effect on electrons in that field. if the field moves, the electrons in it will try to move. conversely, if we have electrons in motion (electric current in a wire, for instance), these moving charges exert a magnetic force (because of their magnet-like property). so, if you glue a magnet onto an axle, and turn the axle, you create a spinning magnetic field. place a length of wire around the spinning magnet, and an electric current (moving electrons) will occur in the wire. this is called induction. if you wrap the wire multiple times around, you increase the amount of current induced. you can verify this if you have a very sensitive ammeter to measure the current with. now we can also take a length of wire and coil it up, then run electric current through it. because of the magnetic properties of electrons, this coil becomes an electromagnet. and we could go even further. take that electromagnet, and spin it (we'll use something called 'slip rings' to keep our wires from twisting up), and you have another spinning magnetic field from which you can induce electricity.

the next thing we'd have to talk about is the idea of direct and alternating current, which we don't have room for here. but there are plenty of good web sites where you can get more information on this topic. here are some i've come across:   ac alternator,  generators,  magnetism.

• Réponse publiée par: hannahleigh
It helps to creating a food or photosenthesis
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Plane vs convex vs concave mirror​...