Time, Motion, Electric current and its effects

Start music   Jan 6 2017 || 2:01 PM

 

Motion and time 

Speed

  • 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

Uniform motion

  • An object moving along a straight line with a constant speed is said to be in uniform motion

 

Non-uniform motion

  • If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform

 

Periodic motion

  • 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

Battery

  • A combination of two or more cells is called a battery

 

Circuit

  • 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

Heating effect

  • 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

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

 

Magnetic effect

  • 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

 

Electromagnets

  • 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