Resistance

Less resistance allows greater current flow.An ordinary light bulb has a resistance of 600 Ω. When placed in a circuit at 120 V, the light bulb draws 0.2 A and lights up as it was designed to do. A certain hairdryer has a resistance of 10.9 Ω. When connected to the same 120 V circuit, the hairdryer draws 11 A. Engineers design the resistance of electrical devices to draw the right current when connected to the right voltage. Every electrical device has a resistance and its resistance determines how much current the device draws in a circuit at the proper voltage. Read the text aloud
Resistors come in many shapes and sizes.  Typical resistors such as these are color coded with a set of bands that indicate their value in ohms.In electronic circuits resistance is created by resistors, such as the ones in the photo on the left. A resistor comes in many standard values of resistance. Resistors are used to control current, voltage, or both in electronic circuits. Read the text aloud
Resistors in circuitsThe symbol for any resistance in a circuit diagram is a zigzag line. The example circuits for the light bulb and hair dryer show each as a zigzag line with the resistance labeled in Ω to the side. Potentiometers are variable resistors and have a knob that is turned to change the resistance. Read the text aloud
Consider what happens when you connect the positive and negative terminals of a 1.5 V battery directly with a piece of wire, which has only a tiny resistance (such as 0.03 Ω). Ohm’s law says that the current should be extremely large—50 A in this case! Such a high current is more than enough current to melt the wire and more than the battery can deliver. That is why short circuits are dangerous! A short circuit presents a low-resistance path for current to flow, allowing too much current. Batteries can safely deliver currents up to 2 or 3 A, and the thin wires in a typical circuit used in the laboratory are chosen to handle this amount of current safely. Read the text aloud Show Internal resistance of a battery
A simple circuit contains only wires, a light bulb with a resistance of 2 Ω, and a 1.5 V battery. How much current flows through the light bulb?
Asked: electric current I
Given: resistance R = 2 Ω, voltage V = 1.5 V
Relationships: Ohm’s law for current: I = V/R
Solution:
I= V R = 1.5 V 2 Ω =0.75 A
Answer: I = 0.75 A.
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