Basic Circuits
Wang Zhikai
Group B6
Pc1222 Lab Report: Basic Circuits
1
Objective
Investigate the relationship among three variables (resistance, current and voltage) in direct
current circuits.
Investigate the circuit characteristics of resistors in series and parallel arrangements.
2
Introduction
When a voltage or potential difference (∆V) is applied across a material, the current (I)
through the material is found to be proportional to the voltage,
I
α
∆V
.
The resistance (R) of
the material is defined as the ratio of the applied voltage and the resulting current, or in
equation format,
R =
.
For many materials, the resistance is constant, or at least
approximately so, over a range of voltages. A material with constant resistance is said to obey
Ohm’s law. The unit for resistance is voltage/amphere (V/A), also known as the ohm (Ω).
In any electrical circuit, Ohm’s law may be applied to either the entire circuit or to an
isolated segment of the circuit. If Ohm’s law is applied to the entire circuit, V refers to the
terminal input voltage supplied by the battery, which acts as a source for the voltage, while R
is the total resistance of the circuit. When Ohm’s law is applied to an isolated segment of the
circuit, V, R and I are the individual voltages, resistances and currents for that segment.
The purpose of this experiment is to investigate Ohm’s law by measuring the voltages,
currents and resistance of a circuit in series, parallel, and combination of the two. We can then
determine if our experimental results deviates from the results predicted by the theoretical
relationship of Ohm’s law. We will then be able to analyse the factors that caused the
deviation, if any.
3
Methodology
Part A: Ohm’s Law and Resistances
Our purpose is to investigate the 3 variables (resistance, voltage and current) involved in a
mathematical relationship called Ohm’s Law. We connected each resistor to the circuit on the
circuit board and measured the current and voltage across the resistor. We then made 10
independent measurements of 10
different resistors using the digital multimeter (DMM).
Part B: Series Circuit
Our purpose is to investigate the current-voltage relationships for resistances in a series circuit.
We measured the resistance of three unequal resistors using the DDM. Next, we set up the three
resistors in series using the PASCO circuit experiment board and measured both the total
voltage/current/resistance as well as the voltage/current/resistance for each individual resistor. The
current is measured by interrupting the circuit in between resistors with the DDM.
Part C: Parallel Circuit
Our purpose is to investigate the current-voltage relationships for resistances in a parallel circuit.
We measured the resistance of three unequal resistors using the DDM. Next, we set up the three