13.9: Relating Current, Voltage, and Resistance
pg. 568
Key Concepts:
1. Connecting loads in series and parallel affects the current, potential
difference, and total resistance.
- Physicist Georg Ohm (1787-1854) discovered the relationship between
current and potential difference.
- Ohm kept the variables of current and voltage constant, but he varied the
length of the conducting wire.
- As length increased, current decreased. Increased length increases
resistance.
- When plotting the data on a graph, a straight line was established.
- The slope of the straight line represents resistance.
- The steeper the slope the greater the resistance.
- The mathematical equation for resistance is R =V/I
Figure 1: A graphical representation of Ohm’s Law
Ohm’s Law: the straight line relationship between voltage and current.
R = V/I
- R is resistance measured in ohms (Ω)
- V is potential difference measured in volts (V)
- I is current measured in amperes (A)
- The relationship is known as Ohm’s Law.
Sample Problem 1: Calculating the Resistance of a load
R = V/I
A load has 1.2 A of current flowing through it. The voltage across the load is
6.0 V. Calculate the resistance of the load.
Given:
Required:
Analysis:
Solution:
Paraphrase:
Sample Problem 2: Calculating the Current through a Resistor
I = V/R
A 110 Ω resistor is connected to a power supply set at 12 V. Calculate the
current going through the resistor.
Given:
Required:
Analysis:
Solution:
Paraphrase:
Sample Problem 3: Calculating the Potential Difference across a Resistor
V = I.R
A toaster oven has a 24.0 Ω resistor that has 5.00 A of current going through
it when the toaster is on. Calculate the potential difference across the resistor.
Given:
Required:
Analysis:
Solution:
Paraphrase:
Evidence of Learning …. Students can
- explain the difference between current, voltage, and resistance.
- calculate the resistance of a load in a circuit.
- calculate the current through a resistor in a circuit.
- calculate the potential difference across a resistor in a circuit.
Check Your Learning
Questions 1 – 9, page 570
Summary:
- The current through a load depends on its resistance and the voltage drop
across it.
- As the potential difference across a load is increased, so is the current
going through the load.
- Electrical resistance can be represented graphically or using Ohm’s
equation.