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When water is heated up-to 100°C it starts boiling and changes into vapor. But we see that even after continuous supply of heat temperature does not rise above the 10°C while boiling of water.

Temperature supplied after 10°C to boiling water is used to change the water into vapor and temperature of water does not rise.

On the other hand we see that when heat is supplied to ice, temperature does not rise above the 0°C, until all ice melts. In this process also the heat supplied to ice after 0°C is used to change of ice into water and temperature of ice does not rise.

• Heat is used in these processes without rise in temperature is known as Latent Heat. The latent heat is used in change of states of matter, such as from solid to liquid or from liquid to gas without rising in temperature.
• Hence, Latent heat is the heat released or absorbed by a body during the process without change in temperature of the system. This happens while change of state of matter meaning a phase transition. Example - Melting of ice, boiling of water.

The particles of solid and liquid are bonded together with great force of attraction, because of which a matter exists in a particular state. When we supply heat to a solid or liquid, the heat is supplied without come in notice is used to break the force of attraction between particles and this heat is not used to increase the kinetic energy of particles. Since, kinetic energy of particles do not increase we do not see any rise in temperature of the system.

The word ‘latent’ is derived from the Latin word ‘Latere” which means “to lie hidden”. Joseph Black introduced the term Latent heat around 1762.

Relation between joule and erg :

1 joule = 1N × 1m

But 1N = 10⁵ dyne

And 1m =100 cm = 10² cm

Hence, 1 joule = 10⁵ dyne × 10²cm

= 10⁷dyne x cm = 10⁷erg

Thus, 1 Joule = 10⁷ erg

Gravitational potential energy is the potential energy possessed by a body due to its position relative to the centre of earth. For a body placed at a height above the ground, the gravitational potential energy is measured by the amount of work done in lifting it up to that height against the force of gravity. Let a body of mass m be lifted from the ground to a vertical height h. The least upward force F required to lift the body (without acceleration) must be equal to the force of gravity (=mg) on the body acting vertically downwards. The work done W on the body in lifting it to a height h is

W = force of gravity (mg) × displacement (h) =mgh

This work is stored in the body when it is at a height h in the form of its gravitational potential energy.

Gravitational potential energy U = mgh

Let a body of mass m fall down through a vertical height h either directly or through an inclined plane e.g. a hill, slope or staircase. The force of gravity on the body is F = mg acting vertically downwards and the displacement in the direction of force (i.e., vertical) is S = h. Therefore the work done by the force of gravity is W = FS = mgh

(a) Motion.

(b) Position.

Yes, when force is normal to displacement, no transfer of energy takes place.

According to the work-energy theorem, the work done by a force on a moving body is equal to the increase in its kinetic energy.

Kinetic energy = 1/2 × mass ×(velocity)²= 1/2 mv² 

From question. l_iron − l_brass = 10 cm = constant at all temperatures. Let l₀ be length at temperature 0ºC and length l after change in temperature.

\(l^o_{iron}\)− \(l^o_{brass}\) = 10 cm at all temperature

∴ \(l^o_{iron}\) (1 + α_iron∆t) − \(l^o_{brass}\)(1 + α_brass∆t) = 10 cm

\(l^o_{iron}\)\(\alpha^o_{iron}\) = \(l^0_{brass} \)α_brass 

∴ \(\frac{l^o_{iron}}{l^o_{brass}}=\frac{1.8\times10^{-5}}{1.2\times10^{-5}}=\frac{1.8}{1.2}=\frac{3}{2}\)

Then,

\(l^o_{iron}\)- \(l^0_{brass} \) = 10

3x - 2x = 10

x = 10 

Length of iron rod = 3 × 10 = 30 cm

Length of brass rod = 2 × 10 = 20 cm

The difference between is 10cm.

Thermal capacity of a body is the energy required to raise its temperature by 1ºC.

c = \(\frac{Q}{\Delta T}\) / or cal ºC^-1.

In case of a step-up transformer, the e.m.f. across the secondary coil is greater than across the primary coil. So the current in the secondary coil is less than in the primary coil. Therefore to reduce heat loss in the windings, the primary coil is made of thicker wire than the secondary coil.

We use a step-up transformer to push up or step up the voltage of a given a.c. source. 

(i) The speed of rotation of the coil is increased. 

(ii) More powerful magnet is used to increase the strength of magnetic field.

No, a transformer will not work with a D.C. source. 

No, a transformer cannot be used with direct current source. The reason is that with direct current source, there will not be any change in the magnetic flux linked with the primary coil, so no e.m.f. will be induced in the secondary coil.

The core of a transformer is laminated to reduce the energy loss due to eddy currents.

The core of a transformer is made of soft iron because it has high permeability so it provides complete linkage of magnetic flux of the primary coil to the secondary coil. Secondly, the hysteresis loss of energy in soft iron is less. 

The frequency of the alternating e.m.f. depends on the frequency of rotation of the coil.

The functioning of a transformer depends on the phenomenon of electromagnetic induction.

Soap and tooth paste contain bases.

1. Start first aid immediately. 

2. Remove contaminated clothes from the person. 

3. Wash the affected area with plenty of water. 

4. Don’t pierce the blisters. 

5. Shift the person to hospital.

The refractive index is maximum for diamond, i. e., for diamond the refractive index, μ = 2.418.

 (i) Unity (ii) 1.33

1. Do not taste and smell. Do not let it fall on the body. 

2. Use a dropper while transferring acid from bottle. 

3. While adding water to make dilution, pour small quantities of acid slowly into water taken in a beaker. 

4. Use a holder to hold a test tube. 

5. Read the precautions given on the containers of substances.

The horizontal range is maximum for θ = 45º and it is given by

\(R_{max}=\frac{u^2}{g}\)

The maximum height attained,

\(H=\frac{u^2sin^2\,\theta}{2g}\)  ...(i)

Therefore, for  θ = 45º

\(H_{max}=\frac{u^2sin^2\,45^o}{2g}\)   ...(ii)

From the equation (i) and (ii),

\(R_{max}=4R_{max}\)

Advantages of storing foods in plastic containers are :

(a) The plastics do not react with the food stored in them.

(b)The plastics are light weight and are strong.

(c) They are easy to handle and safe.

(d) They are lower in price.

1. Hold a concave mirror such that sunlight falls on it.

2. Take a small paper and slowly move it in front of the mirror until we will get smallest and brightest spot of the Sun. 

3. Find the distance between mirror and image of the Sun that will give the focal length of mirror.

• Edible oil – Arachis hypogea
• Dye – Indigofera
• Fibres -Crotalariajuncea
• Medicine – Trigonella
• Fodder -Trifolium 

Tissue: A group of similar or dissimilar cells having a common origin and co-operating with one another to perform a similar or a set of similar functions is called a tissue. 

Plant tissues have been classified into two fundamental types: 

(1) Meristematic tissue: These are the tissues which are made up of group of immature and similar cells and are in continuous state of division, forming new cells. 

(2) Permanent tissue: These are composed of mature cells which have definite shape, size and functions and have lost the power of divisions.

Pericycle of mature zone.

The different components of xylem are : 

(i) Tracheids: These are elongated annular dead cells with narrow blunt ends. They possess hard lignified walls and wide lumen. They allow rapid movement of sap from one cell to another. 

(ii) Vessels: They are much elongated tubular channels with wide lumen. The vessel elements are joined end to end and have perforated end walls. Vessels allow quick movement of water or sap and also provides mechanical strength. 

(iii) Xylem parenchyma: These are parenchymatous cells associated with xylem. They may be thin walled or thick walled with simple pits. Xylem parenchyma stores food. 

(iv) Xylem fibres: They are sclerenchymatous fibres. They may be distinguished from the tracheids by their thick wall and narrow lumen. Xylem fibres provides mechanical support.

The buds which are present in the axils of leaves and are responsible for forming branches or flowers are called Axillary bud.

Gynoecium : 

Family Fabaceae : Ovary superior, monocarpellary, unilocular with many ovules, style single. 

Family Solonaceae : Ovary superior, bicarpellary, syncarpous, bilocular, placenta swollen with many ovules. 

Family Liliaceae : Ovary superior, tricarpellary syncarpous, trilocular with many ovules, axile placentation.

Anatomy is the study of internal structure of organisms. Plant anatomy includes organisation and structure of tissues.

The permanent tissues are derived from meristematic tissue and are composed of cells, which have lost the ability to divide.

Parenchyma:

• Cells are living and form the fundamental tissue of plants.
• They are distributed in all plant parts and do not have thick walls.

Sclerenchyma:

• Cells are dead and provide mechanical support.
• They are distributed in the hypodermis of monocots, cortex, phloem and xylem and possess thick lignified walls.

Heartwood (Duramen)

1. Represents secondary xylem found in the centre of the stem.

2. Appears dark in colour due to deposition of dyes, tannins, etc.

3. Composed of older secondary xylem.

4. Main function is mechanical and wood is durable as timber.

Sapwood (Alburnum)

1. Represents the secondary xylem which surrounds the heartwood.

2. Appears light in colour.

3. Composed of younger secondary xylem

4. Main function is conduction of water and minerals.

(b) earnestly

I realized at once what offence I had given.

(a) unskilled

My arms were filled and I had not spent fifty cents.

That, no doubt is the reason these little children descended on me like locusts.

(b) diligent

 I bought one big basket for a few annas.