Lab 3: Resistance Measurements and Ohms Law
By:
Eng. Nael S. Dokhan
Eng. Malak E. Al-Ashi
The Islamic University of GazaElectrical Engineering & Smart Systems DepartmentEELE 2110Electric Circuits Laboratory
05/10/2020
• Objective:
• To measure and calculate resistors by several methods.
• Approve ohm’s law practically.
• Learn how to use the various instruments.
Theoretical Background
Instruments that will be used in this lab
1. Multimeter:
• Multimeters are designed to measure several variables, typically voltage, current and resistance.
• In this lab we will use a digital multimeter. It consists of :
• Ammeter which is used to measure A.C or D.C current passing in a branch and is connected in series with the circuit’s elements.
• Voltmeter for measuring the A.C or D.C voltage drop a cross any two point in the circuit, and is connected in parallel.
• Ohmmeter for measuring the resistance, and is connected across theresistant.
Dc Power Supply
Electrical measurements
• All basic electrical circuits consist of three separate but very much related electrical quantities called: Voltage ( V ) Current ( I ) and Resistance ( R ).
Ohms Law Relationship
• By knowing any two values of the Voltage, Current or Resistance quantities we can use Ohms Law to find the third missing value.
Electrical Power in Circuits
• Electrical Power, ( P ) in a circuit is the rate at which energy is absorbed or produced within a circuit.
• A source of energy such as a voltage will produce or deliver power while the connected load absorbs it.
• To find the Power (P):
[ P = V x I ] P (watts) = V (volts) x I (amps) Also:
[ P = V2 ÷ R ] P (watts) = V2 (volts) ÷ R (Ω) Also:
[ P = I2 x R ] P (watts) = I2 (amps) x R (Ω)
Ohms Law Pie Chart
DC measurements
• It includes the average value of a time-varying quantity.
AC measurements
• It includes the rms(root mean square)value of a time-varying(usuallyperiodic)quantity.
Multiples and Sub-multiples
Measurement of Resistance
1. Technical method: It depends on the color of resistance.
• Three bands indicate the nominal value of the resistor and the fourth band indicates the tolerance in value.
• The tolerance band is typically either gold or silver.
• A gold tolerance band indicates that the measured value will be within 5% of the nominal value. The silver tolerance band indicates that the measured value will be within 10% of the nominal value.
Measurement of Resistance
Example
Measurement of Resistance2. Manufactured method: Electrical resistance of an electrical conductor depends on:
• the length of the conductor.
• the material of the conductor.
• the temperature of the material.
• the cross-sectional area of the conductor.
• And can be expressed as:
R =𝜌 𝐿
𝐴
• R = resistance of the conductor (Ω).
• ρ: The resistivity of the material conductor (Ω.m).
• L = length of conductor (m).
• A = cross-sectional area of conductor (m2).
Experimentally
Measurement of Resistance
3. Experimental method:
I. By ohms law.
II. By using Ohmmeter.
III. By using Wheatstone Bridge.
Measurement of Resistance
I. By ohms law:
• Y=mx+a
• When the resistance is constant, the current is directly proportional with voltage.
Measurement of Resistance
a- Connect the circuit as shown.
b- Set the resistor to 1KΩ.
c- Record the value of I(ma) for the voltages in the table.
d- Compute the values of R(KΩ) using OHM Law.
Voltage(v) Current(mA) R
1 v 0.921 mA 1k Ω
2 v 1.835 mA 1k Ω
3 v 2.97 mA 1k Ω
4 v 4.04 mA 1k Ω
5 v 5.04 mA 1k Ω
Measurement of Resistance
0.921
1.835
2.97
4.04
5.04
Vo
ltag
e(v)
Current (mA)
Let’s try on LTspice
Voltage(v) Current(mA) R
1 v
2 v
3 v
4 v
5 v
Plot the curve on LTspice
Measurement of Resistance
II. By using Ohmmeter.
1. Connect the circuit as shown.
2. Measure the value of R (KΩ) directly by connecting the digital multimeter in parallel with the resistor and using it as a ohmmeter.
HW Lab3
a- Connect the circuit as shown.b- Set the resistors to 300Ω and 1200Ω.c- Record the value of I(ma) for the voltages inthe table.(from Ltspice)d- Compute the values of R(Ω) using Ohm’s Law.e. Write your comment.
Voltage(v) Current(mA) R
3 v
6 v
9 v
12 v
15 v
HW Lab3
a- Connect the circuit as shown.b- Set the resistors to 300Ω and 1200Ω.c- Draw the graph between V&I.d. Find the slope.e. Write your comment.
Deadline: 12/10/2020 at 11:59 PM
Good Luck