Similarly, increasing the resistance causes the current to drop for a given voltage, while decreasing the resistance causes the current to rise. That is, if the resistance is high, the current is low, and if the resistance is low, the current is large. This relationship can be seen in the following graph:

As the resistance increases, the current decreases.

This makes sense because a higher resistance means that less of the voltage is being dropped across the resistor, so there will be more left over for the battery. Also, since current goes into a resistor, reducing the resistance increases the current flowing into the resistor.

So far we have only talked about resistors that affect alternating **current (AC**). Resistors also have effects on direct current (DC) but these effects are very different from what we have discussed so far. Since resistors can't change the number of electrons flowing through them, they don't affect the voltage across **a DC circuit element** such as **a light bulb** or battery. However, since resistors do slow down the flow of current, they do reduce the power delivered to the load. A high resistance would cause much of the voltage across it to be dropped across the resistor rather than going into the load, so most of **its power** would be wasted instead of used by the lamp.

- What happens when you increase the resistance to a voltage?
- What happens when you increase the resistance in a circuit?
- How does increasing the resistance in a circuit affect the current in the wire?
- How does voltage affect a circuit?
- What happens to the power of an electric circuit when the resistance decreases?

When you raise the resistance of a circuit, the voltage remains constant while the current across the circuit decreases. The power delivered to the load is proportional to the current through it; thus, if current through the load goes down, then the power it receives will go down as well. Increasing the resistance also increases the voltage dropped across the load itself. So, if you were to keep the other factors constant, then the more resistant the circuit, the less power it will deliver.

Here's an example. Let's say we have a 9V battery connected to a resistor and a light bulb. We know that the power supplied by a battery is fixed at about 7.2W, so if we connect it to a resistor that drops 3V out of 9V, then the power consumed by the light bulb will be about 2.4W. If we now connect another resistor to the circuit, this time making the resistance 4 times greater than before (so 12V out of 9V), then the power consumed by the light bulb will be only 1/12 or 0.083W.

So, we can see that by adding **more resistors** into the circuit we are able to reduce the power drawn from the battery being only a third of what it was before.

**What effect** do you believe raising the resistance in a circuit has on the current in the wire? It will reduce the current. Is the current constant throughout, or does it fluctuate? It's the same thing. The total voltage across **any section** of a resistive load is constant; therefore, the current through **that section** must be constant as well.

You can think of resistance as causing **voltage drops** across it. So if you have one end of the resistor connected to a power source and another end connected to a load, then the voltage across the resistor will be the supply voltage minus the drop across it. If the resistance is high enough, then there won't be a drop large enough to cause an increase in the load voltage.

For example, if you have a 1-volt supply and you connect a 10k resistor between the supply and ground, then the voltage across the resistor will be 9 volts. Since 9 volts less than 1 volt equals 8 volts more than 0 volts, there won't be any current flow through the resistor.

However, if you connect a 100k resistor instead, then the voltage across it will be 8 volts too. Since this is still less than 1 volt, there will still be no current flow through the resistor.

This equation, I = v/r, states that the current I flowing through a circuit is proportional to the voltage (v) and inversely proportional to the resistance (r). In **other words**, increasing the voltage causes an increase in current. However, increasing the resistance causes the current to drop. Therefore, to keep **the current constant**, we must either increase the voltage or decrease the resistance.

Voltage can be thought of as pressure pushing electrons through a conductor. The more voltage there is, the more likely it is for an electron to leave its place in the conductor and travel to another place with **energy conserving**. This means that more current will flow through the conductor.

Resistance is the barrier preventing electrons from moving through a conductor. The higher the resistance, the less likely it is for an electron to cross the gap between **two points** in the conductor.

So, increasing voltage will cause an increase in current, while increasing resistance will cause the current to drop. If you want to test yourself: take a look at my diagram below. It shows the effect of resistance on current.

When a simple voltage source feeds **a single simple resistance**, power consumption in the resistance increases as the resistance lowers because current increases as voltage falls. Taking into consideration the source's internal resistance, however, it will begin to decline at **some time**. At first glance this might not seem significant because reduced resistance means more current and thus increased power consumption. But remember that the voltage source is also reducing **its output**, so there will be times when the resistance is very low yet the power supply is still delivering a full voltage.

The situation becomes much more complicated if we have a circuit with many different resistors. Current will flow through any open circuit or short circuit, so the only way to reduce the power consumed by such a circuit is to make all the components more conductive. This can be done by using better materials or by increasing the number of circuits or transistors on a chip. It is also possible to control the amount of current flowing through each component - for example by using MOSFETs (metal-oxide-semiconductor field-effect transistors) as switches - but this requires additional circuitry.

In general, the power consumption of active circuits will increase as their resistance drops, until a point where further reduction leads to lower voltages and thus inactive components. At this point the power consumption begins to rise again as more energy is needed to keep the circuit awake.