Why the resistance of a current source is zero?

What does a super conducter do?

It has no (zero) resistance - thus current flows without losses.

Why do you replace voltage sources with short circuits and current sources with open circuits in thevenin's theorem?

The equivalent of an inactive Thevenin voltage source is a source with zero voltage between its terminals regardless of the current through it, best represented by a zero resistance, i.e. a short-circuit. The equivalent of an inactive Norton current source is a source through which no current can flow regardless of the voltage across it, best represented by an infinite resistance, i.e. an open circuit.

Why internal resistance of an ideal voltage source is zero and an ideal current source is infinty?

Ideal sources do not exist in reality, they are simply theoretical entities to aid in the process of circuit analysis and design. In actual usage they are used as parts of models of real sources.In a first approximation of a real source we must add internal resistance to the ideal source (at higher levels of approximation other things like parasitic reactances must be added to, but internal resistance is good enough for the first approximation):on a voltage source the internal resistance is added in series with the ideal source to drop some of the voltageon a current source the internal resistance is added in parallel with the ideal source to bypass some of the currentNow the source resistance as seen by the load (yes, that may sound like a strange concept but it is correct) mustequal the internal resistance of the source. To find the resistance of the ideal sources themselves we must analyze the resulting series and parallel circuits so that they meet these criteria: in the series circuit of the real voltage source the sum of the internal resistance and the resistance of the ideal voltage source must be equal to the internal resistance. therefore the resistance of the ideal voltage source must be zero.in the parallel circuit of the real current source the internal resistance in parallel with the resistance of the ideal current source must equal the internal resistance. if the resistance of the ideal current source had any finite value then the resistance of the internal resistance in parallel with the resistance of the ideal current source would be less than the internal resistance. therefore the resistance of the ideal current source must be infinite.

How do you find the current if you have the resistance but not the voltage?

The current will be zero if there is no voltage.

Which device has its characteristics very close to that of an ideal current source?

A: A current source can be defined as a zero impedance source. A battery is essentially a zero impedance since it can provide lots of current with zero volts out

What is the value of internal impedance of ideal current source?

internal resistance is always infinite in ideal current source .the internal resistance is in shunt with current source

Why short circuit and open circuit are equivalent appropriate?

In circuit equivalence, voltage and current sources are respectively equated to short and open ckt because of the very nature of them. A voltage source has zero internal resistance and current source has infinite internal resistance hence their equivalents:-)

What is the relationship between the size of your source and an electric current?

If the source you're talking about is an ideal voltage source, then the amount of current depends on the size of the source and the total resistance of the circuit connected to it. Ohm's Law tells us that the current, I, is directly proportional to the voltage, V, and inversely proportional to the resistance, R: I = V/R So, increasing the voltage increases the current, whereas decreasing the resistance does the same. There are practical limitations to that, however. In the real world, reducing the resistance to zero does not produce infinite current, as suggested by the formula. Infinite current is produced only by "ideal" voltage sources, which don't exist.

When measuring a large current flow should you use a shunt with zero resistance?

It is not a shunt with zero resistance. It is very small, but it is not zero. The large current develops a small voltage across the small resistance. Measuring that small voltage gives you a proportional measurement of the current.

What resistance would produce a current of 25 ampers?

resistance does not produce currents . you need source (like voltage source , current source ,or , discharging capacitor) to generate current .

What happens to current in a circuit if the voltage is halved and the resistance stays the same?

the current doubles.. explanation:V=IR hence I=V/R which means that when the supply voltage is constant ,current is inversely proportional to resistance.thus the current doubles. practically speaking when the resistance of the load(fan ,bulb,refrigerator,....) is less ,it draws more current from the source so as to balance the voltage across it.i.e; to maintain the voltage across it as constant. This answer is absolutely correct if you assume that the current comes from a pure voltage source ( voltage source with zero internal resistance). At the other extreme you could have a current source (such as a very large voltage source in series with a very large resistor), and then the current is practically independent of changes if the external resistance is changed (because the change represents a relatively minute change in the overall resistance). With appropriate circuitry it is possible to devise a situation where the current is practically independent of the changing resistance.

Will voltage or current be higher in a circuit during short circuit?

Since a short circuit is, essentially, a zero impedance connection between nodes, the current in a short circuit is limited only by the ability of the source. In the case of an ideal voltage source connected to an ideal short circuit, you would have infinite amperes.