E = IR, also I=E/R and R=E/I
Ohm's law is very simple and it may seem trivial, but its importance in electronics can not be underestimated.
The power (P, in watts) dissipated by the resistor is given by P = IE. This must not exceed the power rating of the resistor or else the resistor will may overheat and be burned up.
Use the slider to change the value of the resistor. Change the battery voltage by typing into the box to the left of the battery symbol. The current and power will be calculated and displayed by the simulation. If the power exceeds 0.5 watts, a warning message will be displayed by the simulation. Resistors with 0.5 watt maximun power rating are the most common type, but higher power resistors are available; usually they are physically larger and cost more that lower-power resistors.