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Chapter Five

Generators and Receivers

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Objectives

  1. Definition of a Generator
  1. U – I graph of Generator
  1. Generators in opposition
  1. U – I graph of Receiver
  1. Definition of a Receiver
  1. Generators in series

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  1. Definition of a generator

Generator: is an electric device that converts forms of energy into electric energy.

Generators called source of electricity.

Ex: thermal power stations, nuclear reactors and dry cells.

A generator has two poles positive and negative.

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  1. Definition of a generator
  • In Generator: The current enters through the negative (-) pole and leaves through the positive (+) pole.
  • A generator is characterized by its electromotive force (e.m.f) E and its internal resistance r.
  • Representation of Generator: G( E, r)

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  1. Current – Voltage Characteristic of a Generator

Set up the circuit of the following figure.

Give the rheostat’s cursor different positions; read the indications of the voltmeter and the Ammeter and record them in a table.

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  1. Current – Voltage Characteristic of a Generator

Plot the graph of V as a function of I; we obtain:

We observe a straight Line of negative Slope and NOT passing through the origin.

This straight Line is called the Current – voltage Characteristic of the generator.

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  1. Current – Voltage Characteristic of a Generator

The equation of the St. Line is U = -kI + b; where k is slope (k=r) and b = E is constant.

 

The: characteristic of a generator are:

  • electromotive force (E).
  • The internal resistance (r).

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  1. Current – Voltage Characteristic of a Generator

To determine the characteristics of an active dipole X, we connect a rheostat across its terminals. A voltmeter and an ammeter are connected in the circuit to determine the voltage U across the terminals of X and intensity of the current I traversing it.

The values of U and I are given in the table below.

I(A)

0.1

0.2

0.3

0.4

0.5

U(V)

5.8

5.4

5

4.6

4.2

Example 1:

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  1. Current – Voltage Characteristic of a Generator
  1. Draw a figure of the electric circuit.
  2. Plot the graph of U as a function of I

Scale: x-axis: 1cm→0.05A and y – axis: 1cm→0.1V.

  1. The dipole X is a generator. Justify.
  2. Determine the equation of (U – I ) characteristic curve of X.
  3. Find the electromotive force E and the internal resistance r.

Example 1:

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  1. Current – Voltage Characteristic of a Generator

Solution of Example 1:

  1. Draw a figure of the electric circuit.

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  1. Current – Voltage Characteristic of a Generator

Solution of Example 1:

  1. Plot the graph of U as a function of I

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  1. Current – Voltage Characteristic of a Generator
  1. The dipole X is a generator. Justify.

The (U – I ) graph of the dipole X is a decreasing line and NOT passing through the origin.

So X is a generator.

Solution of Example 1:

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  1. Current – Voltage Characteristic of a Generator

 

Solution of Example 1:

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  1. Current – Voltage Characteristic of a Generator

 

Solution of Example 1:

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  1. Definition of recevires:

A Recevires: is an electric device that converts consumed the electric energy into other form of energy.

Ex: fan, heater, electrolytic cell and Lamp.

A Receiver is characterized by two quantities, its back electromotive force (back e.m.f) E’ and internal resistance r’. (E’; r’).

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  1. Current – Voltage Characteristic of a Receiver

Set up the following circuit

Give the rheostat’s cursor different positions; read the indications of the voltmeter and of the Ammeter then tabulate the values.

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  1. Current – Voltage Characteristic of a Receiver

Plot the graph of V as a function of I; we obtain:

We observe a straight Line of positive Slope and NOT passing through the origin.

This straight Line is called the Current – voltage Characteristic of the Receiver.

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  1. Current – Voltage Characteristic of a Generator

 

 

 

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  1. Generator in Opposition

If we have two generators in opposition:

The generator with smaller electromotive force plays the role of a receiver.

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  1. Generator in Series

Two generators G1 (6V, 2Ω), G2 (18V, 1Ω) are connected with a resistor of resistance R = 20Ω as shown in the adjacent figure.

Example 2:

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  1. Generator in opposition
  1. Determine which of the two generators act as a receiver.
  2. Deduce the direction of the current passing through this circuit.
  3. Suppose that the magnitude of the current passing through this circuit is I = 0.5 A.
  4. Calculate the voltage across G1.
  5. Calculate the voltage across G2.
  6. Calculate the voltage across R.
  7. Specify the U-I characteristic of G1

Example 2:

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  1. Generator in opposition
  1. Determine which of the two generators act as a receiver.

The two generators are connected in opposition then the one with smallest E play the role of receiver.

So G1 is a receiver.

Solution of the Example 2:

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  1. Generator in opposition
  1. Deduce the direction of the current passing through this circuit.

Solution of the Example 2:

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  1. Generator in opposition

 

Solution of the Example 2:

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  1. Generator in opposition

 

Solution of the Example 2:

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  1. Generator in opposition:

 

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Grade 10 Solving problems 2019 – 2020

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The aim of this exercise is to determine the electromotive force E and the internal resistance r of generator G.

An experiment is used to draw the I-V characteristic curve of G represented in the adjacent figure ( figure next slide).

Exercise 1:

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Grade 10 Solving problems 2019 – 2020

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  1. Draw the circuit diagram.
  2. Find the equation of the given straight line.
  3. Deduce the values of E and R.

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Grade 10 Solving problems 2019 – 2020

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  1. Draw the circuit diagram.

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Grade 10 Solving problems 2019 – 2020

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Grade 10 Solving problems 2019 – 2020

  1. Deduce the values of E and R.

The general equation of generator is U = -rI +E

Compare with the equation of St. Line U =-0.6I +6.16

E= 6.16V and r = 0.6Ω.

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Grade 10 Solving problems 2019 – 2020

Exercise 2:

generators G1 (E1, r1) and G2 (E2, r2) are given in the graph of the figure below. Graph (1) for G1 and graph (2) for G2

The current voltage characteristics of two

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Grade 10 Solving problems 2019 – 2020

  1. Define electromotive force of a generator.
  2. Determine the two characteristics for each of the generators G1 and G2.
  3. The expression of the voltage V across an electric component (D) as a function of the electric current I flowing in the circuit is: V=4I+8
  4. What is the nature of the component (D)? Justify.
  5. Determine its characteristics.
  6. Draw on the same graph the curve of (D).

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Grade 10 Solving problems 2019 – 2020

Solution of Exercise 2:

  1. Define electromotive force of a generator.
  2. e.m.f (E): is the energy provided by the generator per coulomb of charge passing through it.
  3. It is equal to potential difference across the generator when no current is flowing.
  4. It is Expressed in volts (V).

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Grade 10 Solving problems 2019 – 2020

Solution of Exercise 2:

 

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Grade 10 Solving problems 2019 – 2020

Solution of Exercise 2:

 

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Grade 10 Solving problems 2019 – 2020

Solution of Exercise 2:

  1. Draw on the same graph the curve of (D).

 

 

 

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Quiz in physics (9 points)

Chapter 5: Generators & Receiver

Time: 15 min

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Grade 10 Quiz in Physics Time: 20min

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To know the nature of two electric loads D1 and D2 we connect them in series with DC generator of electromotive force E and internal resistance r=2Ω.

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Grade 10 Quiz in Physics Time: 20min

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Two voltmeters V1 and V2 are connected across the terminals of D1 and D2 and an ammeter A is connected as shown in the figure. The table below represents the readings of V1, V2, and A

I (A)

0.1

0.2

0.3

0.4

0.5

0.6

V1 (V)

1

2

3

4

5

6

V2 (V)

4

4.5

5

5.5

6

6.5

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Grade 10 Quiz in Physics Time: 20min

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  1. Trace the I-V characteristic curves of the two electric loads D1, and D2. ( 2point).

Scale: x – axis: 1cm→ 0.1A & y – axis: 1cm→ 1V

  1. Indicate with justification the nature of the electric loads D1 and D2. (1.5point).
  2. Find the equation of the two graphs that correspond to D1 and D2. (2point)
  3. Deduce the characteristics of D1 and D2. (1.5point)
  4. For I=0.3A. Determine, by applying the law of addition of voltages, the value of E of the generator. (2point)

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Grade 10 Quiz in Physics Time: 20min

 

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Grade 10 Quiz in Physics Time: 20min

  1. Indicate with justification the nature of the electric loads D1 and D2.
  2. D1 is a resistor since the shape of the graph is a straight line passing through the origin.
  3. D2 is a receiver since the shape of the graph is an increasing straight line and NOT passing by origin.

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Grade 10 Quiz in Physics Time: 20min

 

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Grade 10 Quiz in Physics Time: 20min

 

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Grade 10 Quiz in Physics Time: 20min

 

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Grade 10 Quiz in Physics Time: 20min

 

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End of Chapter Five