Electricity and Circuit – Electricity Conductors and Insulators
* Materials that allow electricity to pass through them are called conductors.
* Materials that do not allow electricity to pass through there are called insulators.
* We need conducting materials to make electrical circuits.
* Air is an insulator
* All electrical appliances are covered with insulating materials to protect us from electric shocks.
Electric Current and Its Effects – Electric Components
* A circuit diagram is a simplified pictorial representation of an electrical circuit that uses standard symbols for electric components.
* We use symbols to represent electric components, as symbols are standard, and are easy to understand and draw.
* There are two symbols for the positions of the switch, one for the ‘on’ position and the other for the ‘off’ position.
* The positive terminal of a cell is represented by a longer line and the negative terminal is shown by a short line.
* An electric circuit is a closed path formed by the interconnection of electric components through which an electric current can flow.
* A circuit is said to be incomplete, or open, when current does not flow through it.
* A circuit is said to be incomplete, or closed, when current does flow through it.
* A battery is a combination of two or more cells.
* A battery is formed by connecting the positive terminal of a cell to the negative terminal of the next cell n the combination.
* The symbol fro a battery has long lies showing the positive terminals and the short, thick lines showing the negative terminals of each cell, alternately drawn one after the other.
* We use batteries in many devices such as motorcycles, torch lights, mobile phones, wristwatches, calculators and many more.
* Batteries are marked ‘+’ and ‘-‘ to help you find the positive and negative terminals easily.
* We use a cell holder in order to connect multiple cells to prepare batteries
Electric Current and its Effect – The Magnetic Effect of Electri Current
* When electric current is passed through a wire wound around an iron bar, the bar behaves like magnet.
* The magnetic effect of electric current was observed by Danish Scientist Hans Christian Oersted.
* The needle of a magnetic compass deflects when it is brought close to a wire in which electric current is flowing.
* Very strong electromagnets can be used for carrying heavy loads.
* Electromagnets are also used in the field of medicine and i toys.
* One of the common uses of an electromagnet is the electrical bell.
Working of an electric bell:
* When the switch is ON, electric current flows through the coil on an iron core, and its acts as an electromagnet.
* The iron core, which now is an electromagnet, attracts the hammer towards it.
* The hammer hits the bell and produces a sound.
* When the hammer moves towards the iron core, the circuit breaks at the screw contact. at this point, the iron core is not an electromagnet any more.
* The spring pulls the hammer back to its original position. The hammer touches the contact screw again to complete the circuit.
* Current flows through the coil again and the hammer strikes the bell again.
Electricity – Current Electricity – Basics
* Electricity current is uniform flow of charges in a particular direction.
* The rate of flow of charge o uniform motion of electrons:
( I = \frac{Q}{t} )
* Potential difference is the work done in moving a unit charge between two points in an electric field against the direction of force:
(v = \frac{W}{Q} )
* Electric resistance is the opposition to the flow of electrons by the conductor.
Factors affecting electric resistance are:
* The length of the conductor
* The cross sectional area of the conductor
* The resistivity of conductor material
* The temperature of the conductor
Thus, ( R = p \frac{1}{A} )
* Resistivity of a material is the resistance offered by a conductor having unit length and unit area of cross section.
Ohm’s law states that the current passing through a conductor is :
* Direct proportional to the voltage in the conductor and
* Inversely proportional to the resistance of the conductor.
Thus, I = \frac{v}{r}
Electricity – Current Electricity – Circuits
* In parallel circuits:
V = V1 = V2 = V3
Itotal = I1 + I2 + I3
\frac{1}{Req} = \frac{1}{ R_{1} } + \frac{1}{ R_{2} } + \frac{1}{ R_{3} }
Elements of Earth’s Magnetic Field
* The three elements of the earth’s magnetic field at any point are:
1. Declination (D)
2. Angle of dip or the inclination (I)
3. Horizontal component of the earth’s magnetic field (HE)
* The acute angle between the geographical and the magnetic meridian at a point is known as the declination of that point.
* Inclination is the angle that the earth’s total magnetic field makes with its horizontal surface at a given point.