#### Topics

##### Force, Work, Power and Energy

##### Work, Power and Energy

##### Machines

##### Force

##### Light

##### Refraction of Light Through Plane Surface

##### Spectrum

##### Refraction of Light Through a Lense

##### Sound

##### Electricity and Magnetism

##### Current Electricity

- Concept of Current Electricity Numericals
- Ohm’s Law
- Concepts of Emf
- Resistances in Parallel
- Electric Potential Difference
- Concepts of Pd (V), Current (I), Resistance (R) and Charge (Q).
- Internal Resistance
- Resistors in Series
- Current Electricity
- Alternating Current (A.C.) Generator
- Electric Potential and Potential Difference

##### Electrical Power and Energy and Household Circuits

- Concept of Electrical Power and Household Circuits Numericals
- Household Circuits - Colour Coding of Wires
- Household Circuits - Three-pin Plugs
- Household Circuits - Safety Precautions
- Earthing (Grounding)
- Fuses
- Electric Switch
- Household Circuits – Main Circuit
- Electrical Energy and Power
- Electric Power
- Alternating Current (A.C.) Generator
- Current Electricity
- Resistors in Series

##### Electro Manetism

##### Heat

##### Modern Physics

#### notes

**Scientific concept of work:**

- To understand the way we view work and define work from the point of view of science, let us consider some situations:
- Push a pebble lying on a surface. The pebble moves through a distance. You exerted a force on the pebble and the pebble got displaced. In this situation work is done.
- A girl pulls a trolley and the trolley moves through a distance. The girl has exerted a force on the trolley and it is displaced. Therefore, work is done.
- Lift a book through a height. To do this you must apply a force. The book rises up. There is a force applied on the book and the book has moved. Hence, work is done.

A closer look at the above situations reveals that two conditions need to be satisfied for work to be done:

(i) a force should act on an object, and

(ii) the object must be displaced.

If any one of the above conditions does not exist, work is not done. This is the way we view work in science.

#### notes

Let a constant force, F act on an object. Let the object be displaced through a distance, s in the direction of the force. Let W be the work done. We define work to be equal to the product of the force and displacement. Work done = force × displacement

W = F s ..(1)

Thus, work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction. in Eq.(1), if F = 1 N and s = 1 m then the work done by the force will be 1 N m. Here the unit of work is newton metre (N m) or joule (J). Thus 1 J is the amount of work.

#### notes

**Work (W)**

**Definition of Work Done:** Work is defined as the product of the force applied on an object and displacement caused due to the applied force in the direction of the force. Work is a scalar quantity. It has no direction of its own but a magnitude.

It is expressed as the product of force and displacement in the direction of force.

W=F x s

Here W= work done on an object

F = Force on the object

s = Displacement of the object

The unit of Work is Newton metre (Nm) or joule (J).

1 Joule is defined as the amount of work done by force of 1 N when displacement is 1 m.