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Density :

• Density of a substance is its mass per unit volume. It is the characteristic property of any substance.
• It is determined in the laboratory by measuring both the mass and the volume of a sample.
• The density is calculated by dividing mass by volume.

7,000 m is the reading is most accurate.

The following table gives the relative error in count of the given measurement:

Clearly measurement (a) is most accurate because the relative error in it is minimum. The fourth measurement i.e., (d) is most precise because it is taken with an instrument having minimum least count among the given measurements.

It is not necessary that a precise measurement has to be more accurate.

Let true value of certain length be 3 cm. This length is measured with a measuring instrument of limit or resolution of 0.1 cm and the measured value is obtained as 3.1 cm. This length is again measured with another measuring instrument of resolution 0.01 cm and the length is measured as 2.8 cm. 

In this case first measurement has more accuracy because it is closer to the true value but less precision because the resolution is only 0.1 cm whereas in the second is it was 0.01 cm.

The second measurement is more accurate as it has been made to the second decimal point.

0.500 m. due to greater number of significant figures.

(i) ms^-1, 

(ii) N, 

(iii) K, 

(iv) mm, 

(v) K^-1 , 

(vi) kgm^{-3 ,} 

(vii) Wh, 

(viii) gs^{-2 .}

6.0 indicates the measurement is correct up to first decimal place, whereas 6.00 indicates that the measurement is correct up to second decimal place. Thus, 6.00 is a more accurate value than 6.0.

Cesium atomic clock.

Type of mirror used in : 

(i) Headlights of a car: Concave mirror Concave mirror is used because light from the bulb placed at the focus of it gets reflected and produces a powerful parallel beam of light to illuminate the road.

(ii) Rear view mirror of vehicles: Convex mirror Convex mirror is used because it always produces a virtual and erect image whose size is smaller than the object. Therefore, it enables the driver to see a wider field of view and traffic behind the vehicle in a small mirror. 

(iii) Solar furnace: Concave mirror Concave mirror has the property to concentrate the sunlight coming from sun along with heat radiation at its focus. As a result, the temperature at its focus increases and the substance placed at the focal point gets heated to a high temperature.

A) isotope of iodine

Correct option is A) Iodine

Correct option is C) A

The force of attraction between molecules of same substance is called the force of cohesion. This force is lesser in liquid and least in gases.

It is the loss in strength of a material caused due to repeated alternating strains to which the material is subjected.

Since its incompressible strain is 0 and Bulk modulus is infinity.

K = \(\frac{stress}{strain}\) = \(\frac{stress}{0}\) = ∞(infinity)

Let 'L' and 'a' be the original length and the area of cross-section of the wire respectively. If on applying a force F, extension produced is l, then

Y = (F/a)/(l/L) = (Fl)/(al)

In the first case, F = T₁ and l = L₁ - L

Therefore, Y = {T₁L}/{a(L₁ - L)}   ...(i)

In the second case, F = T₂ and l = L₂ - L

Therefore, Y = {T₂L}/{a(L₂ - L)}   ...(ii)

From the equations (i) and (ii), we have

{T₁L}/{a(L₁ - L)} = {T₂L}/{a(L₂ - L)}

or, T₁(L₂ - L) = T₂(L₁ - L)

or, L(T₂ - T₁) = T₂L₁ - T₁L₂

or, L = ({T₂L₁ - T₁L₂}/{T₂ - T₁})

(c) (l₁T₂-l₂ T₁)/(T₂-T₁)

Explanation: 

If the original length of the wire be l and the area of the cross-section a, then  

l₁-l = T₁*l/Ya 

And l₂-l = T₂*l/Ya 

Dividing we get, 

(l₁ -l)*T₂ = (l₂-l)*T₁ 

→l₁T₂ -lT₂= l₂ T₁-T₁l 

→l(T₂-T₁) = l₁T₂-l₂T₁

 →l = (l₁T₂-l₂T₁)/(T₂-T₁) 

Hence the option (c).

Incidence should be at right angle to the surface of substance.

Refractive index of air increases with height.

(b) Convex mirror

Lens of short focal length.

When a light ray moves from denser to rarer medium it bends away from normal.

Light ray undergoes total internal reflection.

When angle of incidence is equal to critical angle then angle of refraction will be equal to 90°.

The amount of light entering the eye is controlled by Iris

(a) Blind spot

(a) Positive power – Convex lens.

(b) Negative power – Concave lens.

C) Both A and B

(c) Spectrum

(b) Vitreous humour

Lens A has more power because of its shorter focal length.

Power of a lens.

Convex lens of short focal length causes more bending of light rays passing through it.

A lens which is thick in middle portion and thin at the edges, is called convex lens. This lens converts all the beams of parallel rays of light into a single point, hence it is called a convex lens. The beams of light rays coming parallel to the axis refract from a convex lens and the point where they all are converge is called focal point of the lens, A lens which is thick at the edges and thin in middle portion is called a concave lens. This lens diverge the light beam coming parallel to the axis. Hence it is called concave lens. Light rays passing through lens deviate from their path, hence we can say that lens refract the light rays,

(a) Dr.CV Raman

(d) The light reflected from the object enters our eyes.

(d) Mid plane

(c) Formation of image by mirror

(b) concave mirror

Correct option is B) Oscilatory

Correct option is  B) Stopwatch

Correct option is B) Speedometer

Correct option is A) Meter/second

1. (b) leave

2. (a) protected

3. (b) stopping

4. (c) totally

5. (c) wandering

1.(a) rose

2. (a) eye-catching

3. (c) to call

4. (c) heaven

5. (a) variation

(b) Herbivores are in a broad ecological context not very different from predators.

1. Environment of depths of ocean are characterized by high pressure, low temperature, absence of light, calmness of water, absence of phytoplankton and other producers, scarcity of food and thus animals staying here show many adaptations. 

2. Due to extreme pressure the bodies of deep- sea fish and other animals are very much compressed. 

3. The bony skeletons are much reduced except for jaws. They have watery muscles. Some deep-sea fishes exhibit greatly enlarged eyes which act like telescope. 

4. They are highly effective as in depths there is less light. Their retina is composed of a number of tiers of rods, presumably arranged to absorb all the limited light that enters the eye. However, the eye-size is small. 

5. Some benthic fishes have eyes located on only one side of the body. E.g. Sole fish. 

6. Many deep-sea animals are bioluminescent, i.e. they produce their own light by means of luminous organs. 

7. In anglerfish, the light is used as a bait to attract prey and also for species and sex recognition. 

8. The mouth of deep-sea fish is the enormous, which enables them to gulp large sized prey. 

9. Many of the deep-sea animals have long appendages, abundant spines, stalks or other

1. Thick cuticle on their leaf surfaces 

2. Stomata of desert plants is sunken that is it is in deep pits to minimize loss of water through transpiration. 

3. Desert plants also have a special photosynthetic pathway (CAM - Crassulacean acid metabolism) that enables their stomata to remain closed during daytime. 

4. Some desert plants like Opuntia, have their leaves reduced or they are modified to spines. Loss of leaf surface helps in prevention of transpiration. 

5. Photosynthetic function is taken over by the flattened stems called as phylloclade.