#### Topics

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

##### Force

##### Work, Power and Energy

- Introduction of Work
- Concept of Work
- Measurement of Work
- Work Done by the Force of Gravity (W = mgh)
- Power
- Concept of Energy
- Mechanical Energy and Its Types
- Potential Energy
- Types of Potential Energy
- Gravitational Potential Energy
- Kinetic Energy
- Types of Kinetic Energy
- Conversion of Potential Energy into Kinetic Energy
- Transformation of Energy
- Different Forms of Energy
- Principle of Conservation of Energy
- Theoretical verification of K + U = Constant for a freely falling body
- Application of Principle of Conservation of Energy to a Simple Pendulum

##### Machines

##### Light

##### Refraction of Light Through Plane Surface

- Refraction of Light
- Law of Refraction of Light
- Refractive Index
- Speed of Light
- Relationship Between Refractive Index and Speed of Light (µ = C/V)
- Principle of Reversibility of the Path of Light
- Experimental Verification of Law of Refraction
- Refraction of Light Through a Rectangular Glass Slab
- Multiple Images in a Thick Plane Glass Plate Or Thick Mirror
- Concept of Prism
- Refraction of Light Through a Prism
- Real and Apparent Depth
- Apparent Bending of a Stick Under Water
- Transmission of Light from a Denser Medium (Glass Or Water) to a Rarer Medium (Air) at Different Angles of Incidence
- Critical Angle
- Relationship Between the Critical Angle and the Refractive Index (µ = 1/ Sin C)
- Total Internal Reflection
- Total Internal Reflection in a Prism

##### Spectrum

- Deviation Produced by a Triangular Prism
- Colour in White Light with Their Wavelength and Frequency Range
- Concept of Prism
- Dispersion of Light Through Prism and Formation of Spectrum
- Electromagnetic Spectrum
- Different Radiation of Electromagnetic Spectrum
- Gamma Rays
- X rays
- Ultraviolet Radiations
- Visible Light
- Infrared Radiations
- Micro Waves
- Radio Waves
- Scattering of Light and Its Types
- Applications of Scattering of Light

##### Refraction of Light Through a Lense

- Lens
- Action of a Lens as a Set of Prisms
- Spherical Lens
- Refraction of Light Through the Equiconvex Lens and Equiconcave Lens
- Guideline for Image Formation Due to Refraction Through a Convex and Concave Lens
- Formation of Image by Reflection: Real and Virtual Image
- Images Formed by Sperical Lenses
- Concave Lens
- Images Formed Due to Refraction Through a Concave Lens
- Convex Lens
- Images Formed Due to Refraction Through a Convex Lens
- Differentiation Between Concave and Convex Lens
- Sign Convention for Spherical Lenses
- Lens Formula
- Magnification Due to Spherical Lenses
- Power of a Lens
- Magnifying Glass Or Simple Microscope
- Experimental Determination of Focal Length of Convex Lens

##### Sound

- Sound
- Difference Between the Sound and Light Waves
- Characteristics of a Sound Wave
- Reflection of Sound
- Echoes
- Natural Vibrations
- Damped Vibrations
- Forced Vibrations
- Resonance
- Demonstration of Resonance
- Properties of Sounds
- Loudness and Intensity
- Pitch (or shrillness) and frequency
- Audibility and Range
- Quality (Or Timbre) and Wave Form
- Noise Pollution
- Noise and Music
- Sound (Numerical)

##### Electricity and Magnetism

##### Current Electricity

- Electric Charge
- Electric Current
- Electric Circuit
- Potential and Potential Difference
- Resistance (R)
- Ohm's Law
- Experimental Verification of Ohm’s Law
- Ohmic and Non-ohmic Resistors
- Electrical Resistivity and Electrical Conductivity
- Choice of Material of a Wire
- Superconductors
- Electro-motive Force (E.M.F.) of a Cell
- Terminal Voltage of a Cell
- Internal Resistance of a Cell
- System of Resistors
- Resistors in Series
- Resistances in Parallel
- Series Connection of Parallel Resistors
- Parallel Connection of Series Resistors

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

- Electrical Energy
- Measurement of Electrical Energy (Expression W = QV = Vlt)
- Electrical Power
- Commercial Unit of Electrical Energy
- Power Rating of Appliances
- Household Consumption of Electric Energy
- Effects of Electric Current
- Heating Effect of Electric Current
- Transmission of Power from the Power Generating Station to the Consumer
- Household Electrical Circuits
- House Wiring (Ring System)
- Electric Fuse
- Miniature Circuit Breaker (MCB)
- Electric Switch
- Circuits with Dual Control Switches (Staircase Wire)
- Earthing (Grounding)
- Three-pin Plug and Socket
- Colour Coding of Live, Neutral, and Earth Wires
- High Tension Wires
- Precautions to Be Taken While Using Electricity

##### Electro Magnetism

- Effects of Electric Current
- Magnetic Effect of Electric Current
- Magnetic Field Due to a Current Carrying Straight Conductor
- Rule to Find the Direction of Magnetic Field
- Magnetic Field Due to Current in a Loop (Or Circular Coil)
- Magnetic Field Due to a Current Carving Cylindrical Coil (or Solenoid)
- Electromagnet
- Making of an Electromagnet
- Permanent Magnet and Electromagnet
- Applications of Electromagnets
- Force on a Current Carrying Conductor in a Magnetic Field
- Direct Current Motor
- Electromagnetic Induction
- Faraday's Laws of Electromagnetic Induction
- Alternating Current (A.C.) Generator
- Distinction Between an A.C. Generator and D.C. Motor
- Types of current: Alternating Current (A.C.) and Direct Current (D.C.)
- Transformer
- Types of Transformer

##### Heat

- Heat and Its Unit
- Temperatures
- Heat and Temperature
- Heat Capacity Or Thermal Capacity
- Specific Heat Capacity
- Relationship Between the Heat Capacity and Specfic Heat Capacity
- Calorimetry and Calorimeter
- Natural Phenomena and Consequences of High Specific Heat Capacity of Water
- Some Examples of High and Low Heat Capacity
- Change of State of Matter
- Concept of Melting (Fusion)
- Concept of Freezing (Solidification)
- Concept of Boiling (Vaporization)
- Concept of Condensation (Liquefaction)
- Latent Heat and Specific Latent Heat
- Specific Latent Heat of Fusion of Ice
- Explanation of Latent Heat of Melting on the Basis of Kinetic Model

##### Modern Physics

- Atoms: Building Blocks of Matter
- Structure of an Atom
- Discovery of Charged Particles in Matter
- Nucleus
- Atomic Mass
- Atomic Number (Z), Mass Number (A), and Number of Neutrons (n)
- Isotopes
- Isobars
- Isotones or Isoneutronic
- Radioactivity
- Radioactivity as Emission of Alpha, Beta, and Gamma Radiations
- Properties of Alpha Particles
- Properties of Beta Particles
- Properties of Gamma Radiations
- Changes Within the Nucleus in Alpha, Beta and Gamma Emission
- Alpha Decay (Alpha Emission)
- Beta Decay (Beta Emission)
- Gamma Decay (Gamma Emission)
- Uses of Radioactive Isotopes
- Radiation
- Nuclear Energy
- Safety Precautions While Using Nuclear Energy
- Nuclear Fission
- Nuclear Fusion
- Distinction Between the Radioactive Decay and Nuclear Fission
- Distinction Between the Nuclear Fission and Nuclear Fusion

#### 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

**Work:**

**“The work done by the force is defined to be the product of component of the force in the direction of the displacement and the magnitude of this displacement.”**

The work W done by a constant force F when its point of application undergoes a displacement s is defined to be

`W=bar F.bar s=F s cos θ`

where θ is the angle between `bar F` and `bar s` as indicated in figure. Only the component of `bar F` along s, that is fcos θ, contributes to the work done.

Work is a scalar quantity and its SI unit is the joule (J). From the above equation, we see that

1 J = 1 Nm = 10^{7} erg

In terms of rectangular components, the two vectors are

`bar F= F_x hat i + F_y hat j + F_ z hat k`

and `bar s = Δx hat i +Δ y hat j+Δ z hat k`

hence, the above equation may be written as

`W=F_x Δx + F_y Δy + F_z Δz`

The work done by a given force on a body depends only on the force, the displacement, and the angle between them. It does not depend on the velocity or the acceleration of the body, or on the presence of other forces.

When several forces act on a body one may calculate the work done by each force individually. The net work done on the body is the algebraic sum of individual contributions.

`W_"net" = bar F_1. bar S_1 + bar F_2. bar S_2 +.........+ bar F_n. bar S_n` or

`W_"net" = W_1 + W_2 +............ + W_n`**No work is done if:**

1. The displacement is zero

2. The force is zero.

3. The force and displacement are mutually perpendicular.

**Positive, Negative and Zero Work:-**Work done by a force may be positive or negative depending on the angle θ between the force and displacement. If the angle θ is acute (`θ < 90^o`), then the work done is positive and the component of force is parallel to the displacement.

If the angle θ is obtuse (`θ > 90^o`), the component of force is antiparallel to the displacement and the work done by force is negative.

**Application 1**

When a person lifts a body from the ground to some higher position, the work done by the lifting force (i.e. the force applied by the person) is positive since force (vector) and displacement (vector) are along the same (vertically upward) direction and hence,**θ = 0 cos θ =1**

However, the work done by the gravity (or the force by the earth on the body) is negative since force (vector) and displacement (vector) are oppositely directed and hence **θ = 180 ^{o} cos θ = −1**.

**Application 2**

A box is moved over a horizontal path by applying force F = 60 N at an angle θ = 30^{o} to the horizontal. What is the work done during the displacement of the box over a distance of 0.5 km.**Solution:**

By definition, W = F s cos θ

Here F = 60 N; s = 0.5 km = 500m; θ= 30^{o}

W = (60)(500) cos30^{o} = 26 kJ

#### 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.

#### description

- Definition of work
- Units of work
- Relationship between joule and erg
- Positive, Negative, and Zero Work