1 DC ELECTRICAL CIRCUITS ELECTRICAL FORCE

2 DC ELECTRICAL CIRCUITS Current will not flow in a circuit unless an external force is applied. A popular name for external force is EMF or electromotive force. Current will not flow in a circuit unless an external force is applied. A popular name for external force is EMF or electromotive force. EMF CAUSES ELECTRONS TO FLOW IN A CLOSED CIRCUIT.

3 DC ELECTRICAL CIRCUITS Another name for electrical force is potential difference, this name describes the characteristics of EMF in an open circuit. In the circuit below the switch is open so current can’t flow but the battery is still producing the same electrical pressure so the potential for producing current flow exists. Another name for electrical force is potential difference, this name describes the characteristics of EMF in an open circuit. In the circuit below the switch is open so current can’t flow but the battery is still producing the same electrical pressure so the potential for producing current flow exists.

4 DC ELECTRICAL CIRCUITS In this case potential means the possibility of doing work. In a battery there are two different charges, the negative charges are attracted to the positive terminal, this force is called potential difference. A potential can exist between two charges of the same polarity if they have different magnitudes. In this case potential means the possibility of doing work. In a battery there are two different charges, the negative charges are attracted to the positive terminal, this force is called potential difference. A potential can exist between two charges of the same polarity if they have different magnitudes.

5 DC ELECTRICAL CIRCUITS Electrons will flow from the greater negative charge to the lesser negative charge. Electron flow will ceases as soon as the two charges become equal. Electrons will flow from the greater negative charge to the lesser negative charge. Electron flow will ceases as soon as the two charges become equal. A POTENTIAL DIFFERENCE OF TWO MILLION ELECTRONS.

6 DC ELECTRICAL CIRCUITS Another term that is used interchangeably with EMF and potential difference is voltage. Technically voltage is a measure of EMF or potential difference. The metric unit of energy is the joule. Another term that is used interchangeably with EMF and potential difference is voltage. Technically voltage is a measure of EMF or potential difference. The metric unit of energy is the joule.

7 DC ELECTRICAL CIRCUITS One joule equals.738 foot pounds. A foot pound is the amount of work that is required to lift one pound a distance of one foot. Thus a joule is the amount of work required to lift ¾ of a pound one foot off the ground. One joule equals.738 foot pounds. A foot pound is the amount of work that is required to lift one pound a distance of one foot. Thus a joule is the amount of work required to lift ¾ of a pound one foot off the ground.

8 DC ELECTRICAL CIRCUITS One volt is the EMF required to cause one joule (.738 foot pounds) of work to move on coulomb of charge (6.25 x electrons) from one point to another. Voltage is represented by the symbol (E) when used in formulas. The letter (V) is used to express the amount of EMF in a circuit, i.e. the electrical outlets are 120V. One volt is the EMF required to cause one joule (.738 foot pounds) of work to move on coulomb of charge (6.25 x electrons) from one point to another. Voltage is represented by the symbol (E) when used in formulas. The letter (V) is used to express the amount of EMF in a circuit, i.e. the electrical outlets are 120V.

9 DC ELECTRICAL CIRCUITS There are six basic methods for producing electricity: 1. MAGNETISM2. CHEMICAL3. PRESSURE4. HEAT5. FRICTION6. LIGHT

10 DC ELECTRICAL CIRCUITS Magnetism is the most widely used method for producing electrical power. Well over 99% of all electrical power available today is produced by this method. When a conductor is moved through a magnetic field an EMF is produced, this is done by the use of generators and is called AC, alternating current. Magnetism is the most widely used method for producing electrical power. Well over 99% of all electrical power available today is produced by this method. When a conductor is moved through a magnetic field an EMF is produced, this is done by the use of generators and is called AC, alternating current.

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12 DC ELECTRICAL CIRCUITS The force of the magnetic field and the movement of the conductor provide the energy necessary to free electrons in the conductor. The second most popular method of producing electricity is by chemical means, batteries use a chemical process to produce EMF. The force of the magnetic field and the movement of the conductor provide the energy necessary to free electrons in the conductor. The second most popular method of producing electricity is by chemical means, batteries use a chemical process to produce EMF.

13 DC ELECTRICAL CIRCUITS Current flows from the negative terminal of a battery to the positive terminal! Batteries can be classified by 2 categories: 1.PRIMARY CELLS or DRY CELL 2.SECONDARY CELLS or WET CELL Current flows from the negative terminal of a battery to the positive terminal! Batteries can be classified by 2 categories: 1.PRIMARY CELLS or DRY CELL 2.SECONDARY CELLS or WET CELL

14 DC ELECTRICAL CIRCUITS Primary cells (dry cells) usually only provide 1.5 to 9 volts and aren’t rechargeable, they can be sub categorized as: CARBON ZINC CELLS ALKALINE CELLS LITHIUM CELLS

15 DC ELECTRICAL CIRCUITS Secondary cells (wet cells) are batteries that can be recharged by applying a reverse charge, these type of batteries can be sub categorized into: LEAD ACID BATTERIES NICKEL-CADMIUM (NI-CAD)

16 DC ELECTRICAL CIRCUITS Batteries can be connected together to increase voltage and/or current. They can be connected in series, parallel or series parallel. Connecting batteries in series increases voltage. Connecting batteries in parallel increases current. Batteries can be connected together to increase voltage and/or current. They can be connected in series, parallel or series parallel. Connecting batteries in series increases voltage. Connecting batteries in parallel increases current.

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19 DC ELECTRICAL CIRCUITS To increase both current and voltage batteries can be connecting in a series/parallel configuration.