Changing resistor

[nForce]

So I can change a 0.25 W resistor with a 2 W with the same resistance, but I can't change 2 W resistor with 0.25 W? Is this is same as capacitance and voltage at capacitors?

[ArthurDent]

There needs to be more context but you can't almost randomly interchange components.

Consider a 12 volt 1/4 watt incandescent lamp and a 120 volt 2 watt incandescent lamp. If you try to connect the 12 volt lamp to the 120 volt circuit, it will be very bright for a split second before it burns out. The voltage rating on a capacitor should not be exceeded and a capacitor shouldn't be used above perhaps 80% of its rating. Google can be of help here.  http://www.learningaboutelectronics.com/Articles/What-does-the-voltage-rating-on-a-capacitor-mean .

[Kirill V.]

The Maximum power dissipated of resistor means that this resistor able to dissipate a certain amount of heat into the environment per unit time (this is the power) for a long time. At the same time its main parameters do not degrade.
Your question is not quite clear to me, could you formulate it in more detail?

[Zero999]

So I can change a 0.25 W resistor with a 2 W with the same resistance, but I can't change 2 W resistor with 0.25 W? Is this is same as capacitance and voltage at capacitors?

Generally yes, in DC/low frequency applications a low power resistor can be exchanged for a much higher power one of the same resistance. However, at high frequencies, when the parasitics become significant, replacing small components with physically larger ones will create problems.

[andy3055]

So I can change a 0.25 W resistor with a 2 W with the same resistance, but I can't change 2 W resistor with 0.25 W? Is this is same as capacitance and voltage at capacitors?

A simpler way to think of this would be to use the general formula W=VxI or I=W/V.

Given that V remains constant, W is dependent on I. If W is lower, it means I has to go down as well. What that means is that the resistor with the lower W can pass only a lower current. Resistors are built so that they have different wattages for any given resistance as one need not use a physically large component taking up space. Now, to do that, the current carrying capacity has to be reduced. So, in other words, the 0.25 W will not be able to carry the same current as a 2 W resistor as it will over heat or burn down.

I hope this helps.

[TimFox]

Components have specifications and ratings, which are separate.
For a resistor, the normal specifications include nominal resistance, percentage tolerance of that value from part to part in production, and temperature co-efficient (change in resistance with temperature).
The normal ratings include maximum power (without destruction or change in value) and maximum voltage (also without destruction).
The choice of rating (like power) depends on what the circuit will actually or potentially impose on the component.

[GerryR]

"Rule-of-thumb" is to calculate the power that the resistor will use in circuit and use a power value at least 2-1/2 times.  For example, if you calculate that a resistor will dissipate 1/10 W, then a 1/4 W or larger will be fine.