Difference between Voltage source and Current source?
Voltage and current sources are not related by \$V=IR\$. This applies to resistances. However, you can connect a resistor to a voltage and current source, and then see what happens to voltage across the resistor and current through it.

A voltage source will maintain a constant V, regardless of the load connected to it. A current source will maintain a constant I, regardless of the load. Consider what happens as R changes in these two cases:







simulate this circuit &ndash; Schematic created using CircuitLab

For the case on the left, consider the resistance \$R\$, and the voltage across it \$V_R\$, and the current through it, \$I_R\$:

R   Vr  Ir
0Ω  1V  ∞A
1Ω  1V  1A
2Ω  1V  0.5A
3Ω  1V  0.33A
4Ω  1V  0.25A
∞Ω  1V  0A


Now consider the case on the right:

R   Vr  Ir
0Ω  0V  1A
1Ω  1V  1A
2Ω  2V  1A
3Ω  3V  1A
4Ω  4V  1A
∞Ω  ∞V  1A


In all cases, \$V_R = I_R R\$. On the left, \$V_R = 1V\$ (by Kirchhoff's voltage law), so \$I_R\$ is whatever it needs to be to satisfy Ohm's law.

On the right, \$I_R = 1A\$ (by Kirchhoff's current law), so \$V_R\$ is whatever it needs to be to satisfy Ohm's law.

Also notice that 0Ω is equivalent to a short circuit, and ∞Ω is equivalent to an open circuit. In some cases this results in infinite voltage or infinite current, which is an indication that these things can't physically happen. For example, if you actually short out a real voltage source, like a battery, the wire has actually some small resistance. A lot of current flows, but not an infinite current.

If you like, you can think of a voltage source as something that moves current, but adjusts the amount such that a constant voltage is maintained. You can think of a current source as something that adjusts the voltage across itself so that a constant current is moved. Realize of course that you are endowing the power of thought to inanimate objects, which isn't really true. Really all that's happening is that a current or voltage source introduces one constraint to a system of equations that must be solved.

You should also think about what happens when the thing connected is not a resistor. For example, what if it's a diode, like an LED? The voltage source still attempts to maintain a constant voltage, and the current source attempts to maintain a common current, but no longer is the equation being solved \$V=IR\$. That describes the behavior of resistances, but now the equation will be something else, describing whatever it is you have connected.