Notes on Current Electricity | Grade 7 > Science > Electricity | KULLABS.COM

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Every material is made up of an atom and every atom is made up of two types of charged particles. They are protons and electrons. Protons are positively charged and electrons are negatively charged. Different metals like copper, iron, aluminium etc consist of a large number of free electrons. When this free electron flows continuously in a certain direction, electric current is produced. Therefore, current electricity is the continuous flow of electrons. Current electricity is a form of energy. It is used for various purpose. It can be easily converted into heat energy, light energy, sound energy, magnetic energy, etc.

#### Sources of Electricity

Electricity has become one of the important part of human life. It is very difficult to live without electricity. We use various types of electrical appliances such as computer, television, radio, mobile, refrigerator, calculator, watch etc. These appliances make our life easier and comfortable to live. To run all these appliances, we need electrical energy. Electrical energy is also very important to run various industries, factories, transportation systems and many other important things. The devices from which we obtain electricity are called sources of electricity. The three major sources of electricity areas follow,

• Cell
• Photocell or Solar cell
• Dynamo or Generator

#### Electric Circuit

An electric circuit is a path through which an electron from current source or voltage flows. It is also the path made by connecting a cell, a conducting wire and a bulb. There are various things that are required for making an electric circuit which are discussed below,

• Cell or Battery: It is the source of electricity through which we obtain electricity.
• Conducting wire: It is the path or medium through which electric current flows.
• Bulb: A bulb is a device that produces light and heat energy from the electricity. It is also called a load. It shows the effect of electric current.
• Switch: It is a device used to open or close an electric circuit. Source; romariohyman.blogspot.com Fig: Electric Circuit

Open circuit and Closed circuit

An open circuit is a type of circuit in which the switch is made 'OFF' and the bulb does not glow. During this condition, the current cannot flow through the wire. So, the load cannot function when the circuit is opened. Talking about the close circuit, it a type of circuit in which the switch is made 'ON'. In a closed circuit, the bulb glows as the current flows through the circuit continuously.

Symbols used in Circuit Diagrams

While drawing circuit diagrams, we cannot draw all the components used in electric circuit. It is very difficult and takes lots of time to draw the various components like battery, wire, voltmeter,galvanometer etc. So, to save time and for easy, various symbols representing various components used in electric circuit are used. Some of the symbols that are used moslty in an electric circuit are given below,

 S.No. Components Symbols Function 1. Cell Source of electric current 2. Bulb To produce light 3. Wire To make conducting path 4. Load or Resistance To convert electrical energy into other forms of energy like heat and light 5. Galvanometer To detect the current 6. Switch To put the current on or off in the circuit 7. Battery Source of electric current 8. Voltmeter To measure the voltage 9. Ammeter To measure the current

#### Combination of Cells

Cell is also one of the sources of electricity. It produces electric current. We use cell for various purpose. Sometimes we need low voltage and sometimes we need high voltage. To have different voltage, we should connect the cells in different ways. Mainly there are two ways of combination of the cells which are discussed below,

• Series combination: Series combination is a combination of cell in which the positive terminal of the first cell is connected with negative terminal of the second cell and positive terminal of the second cell with the negative terminal of the third cell and so on. Here, the brightness of the cell increases with the increases in number of cell asthe current increases when the number of cell is increased and decreases with the decrease in number of cellas the current decreases when the number of cell is decreased. It is especially done when more current or voltage is required.
In series combination, the total voltage is equal to the sum of the voltage of the individual cells. If V be the total voltage and V1, V2, and V3be the individual voltage of cell C1, C2, and C3 respectively, then the total voltage is given by,
V = V1+ V2 +V3
• Parallel combination: The combination of cells are said to be connected in parallel combination when the positive terminal of all the cells are connected together in one common point and negative terminal of all the cells are connected together in another common point in a circuit is known as parallel combination of the cells. In this combination,the brightness of the light does not increases with increase in number of cells. Here,the bulb glows for longer time than in series combination of the cells. It is especially done when less voltage and high current is required
In parallel combination, the total voltage of the circuit is equal to the individual voltage of each cells.In series combination, the total voltage is equal to the sum of the voltage of the individual cells. If V be the total voltage and V1, V2, and V3be the individual voltage of cell C1, C2, and C3 respectively, then the total voltage is given by,
V = V1= V2= V3

• Current electricity is a form of energy produced due to the continuous flow of electrons through a conductor.
• The devices from which we obtain electricity are called sources of electricity.
• An electric circuit is a path made by connecting a cell, a conducting wire, and a bulb.
• Series combination is a combination of various cells in which  positive terminal of the first cell is connected with a negative terminal of the second cell and positive terminal of the second cell is connected to a negative terminal of the third cell and so on.
• Parallel combination of a cell is the combination of cell in which the positive terminals of all cells are connected to a common point and all the negative terminals are connected to another common point in a circuit.
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### Very Short Questions

If the positive terminal of the first cell is connected to the negative terminal of the second cell and positive terminal of the second cell with the negative terminal of the third cell and so on is called a series combination of the cell.
If the positive terminal of all cells are connected to a common point and all the negative terminals are connected to another common point in a circuit, the combination of cells is called parallel combination.

The things required for making electric circuit are given below,

• Cell or Battery
• Conducting wire
• Bulb
• Switch

There are two types electric circuit. They are discussed below,

• Open circuit: The electric circuit in which no electric current is flowing is called open electric circuit. In such electric circuit, the switch may be in on state. So, there is no any breakage in the wire.
• Closed circuit: The electric circuit in which electric current is flowing is called open electric circuit, the switch may be in off state or there may be breakage in the wire.

The differences between static electricity and current electricity are given below in table,

 Static electricity Current electricity The electricity in which electric charges remain at rest (or stationary) is called electricity. The electricity in which electric charges remain at continuous motion is called current electricity. Static electricity cannot be transferred from one point to another through a conductor. Current electricity can be transferred from one point to another through a conductor.

The differences between series combination and parallel combination of cells are given below,

 Series combinations of cell Parallel combinations of cell The combination of cells in which positive terminal of the first cell is connected to the negative terminal of the second cell, positive terminal of the second cell is connected to negative terminal of the third cell and so on is called series combination of cell. The combination of cells in which positive terminal of all cell are connected to a common point and negative terminals of the same cells are connected to another common point is called parallel combination of cells. In series combination, the total voltage is equal to the sum of individual voltage. In parallel combination, the total voltage is equal to the voltage of each cell.

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• ### The form of energy produced due to the continuous flow of electrons through a conductor is called

Current electricity
Friction
Static electricity
Electric circuit
• ### Which one of the following is not the sources of electricity?

Cell
Dynamo or Generator
Guitar
Photo cell or Solar cell
• ### The path made by connecting a cell, a conducting wire and a bulb is called

Electric wire
Current electricity
Static electricity
Electric circuit
• ### Which one of the following is not required for making an electric circuit?

Bulb
Switch
Cell or battery
Wood
• ### Which one of the following acts as a source of electricity?

Switch
Conducting wire
Bulb
Cell or battery
• ### Which one of the following device converts electrical energy into heat and light energy?

Bulb
Switch
Conducting wire
Cell or battery
• ### When the switch is made 'ON', then the circuit is known as

Half circuit
Null circuit
Closed circuit
Open circuit
• ### When the switch is made 'OFF', then the circuit is known as

Half circuit
Closed circuit
Open circuit
Null circuit

3
4
6
2
• ### The brightness of the bulb ________ with the increase in numberof cells in series combinations of cells.

Becomes zero
Does not glow
Decreases
Increases
• ### The brightness of the bulb ________ with the increase in numberof cells in parallel combinations of cells.

Does not glow
Does not increases
Decreases
Increases
• ### In which combination of cells, the total voltage of the circuit is equal to the voltage due to each cell?

Series combination
None of the given
Parallel combination
Both of them
• ### In which combination of cells, the total voltage of the circuit is equal to the sum of the voltage of the individual cells?

ZigZag combination
Parallel combination
Series combination
None of this
• ### Which combination is used when low voltage and high current is required?

Series combination
Parallel combination
All of them
ZigZag combination
• ### Which combintion is used when more voltage and more current is required?

Parallel combination
All of them
Series combination
ZigZag combination

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