Time, Motion, Electric current and its effects
Motion and time
- The distance covered by an object in a unit time is the speed of the object
- Speed is the total distance covered divided by the total time taken
Speed = Total distance covered ÷ Total time
Types of Motion
- An object moving along a straight line with a constant speed is said to be in uniform motion
- If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform
- Motion that recurs over and over and the period of time period of each recurrence remains the same is called periodic motion. Example: simple pendulum
- The to and fro motion of a pendulum is also called an oscillation
- The time taken by the pendulum to complete one oscillation is called its time period.
- The time period of a given pendulum is always constant.
- This observation led to the development of pendulum clocks
Units of time and speed
- NOTE: The symbols of all units are written in singular
- The basic unit of time is a second
- The standard way to denote speed is meters per second
- The device that measures the distance covered by a vehicle is known as an odometer
Electric current and its effects
- A combination of two or more cells is called a battery
- An electrical device that provides a path for electrical current to flow
- When the switch is in the ‘ON’ position, the circuit is then said to be closed and the current flows throughout the circuit
- When the switch is in the ‘OFF’ position, the circuit is incomplete
Effects of electric current
- The wire gets hot when an electric current passes through it.
- This is the heating effect of the electric current
- The amount of heat produced in a wire depends on its material, length and thickness
- This principle is used in heating elements such as water heater, heating iron, induction stove and electric fuses
- Wires made from some special materials melt quickly and break circuit when large electric currents pass through them.
- These wires are used for making electric fuses
- This fuse, is a safety device which prevents damages to electrical circuits and possible fires by breaking the circuit when excess electric current passes through
- However, nowadays Miniature circuit breakers (MCBs) are increasingly being used in place of fuses
- Scientist Hans Christian Oersted noticed the deflection of compass needle every time the current was passed through the wire
- It was concluded that when electric current passes through a wire, it behaves like a magnet
- Similarly, when electric current passes through a coil, it behaves like a magnet
- When the electric current is switched off, the coil generally loses its magnetism.
- Such coils are called electromagnets
- Electromagnets are very strong and can lift heavy loads
Uses of electromagnets
- To separate magnetic material from the junk
- Doctors use tiny electromagnets to take out small pieces of magnetic material that have accidentally fallen in the eye.
- In electric bell