(i) The speed of light in a medium is low if the refractive index of the medium is high and vice versa.
(ii) When light travels from a denser medium into a rarer medium, the refracted ray is bent away from the normal drawn to the interface.
(iii) When light travels from a rarer medium into a denser medium, the refracted ray is bent towards the normal drawn to the interface.

(i) Striking a hammer on a nail.
(ii) Hitting cricket ball with the bat.
(iii) We get hurt more while we slip down on a concrete floor than on a mud floor.
(iv) Both the floors experience same amount of change in momentum. But in concrete floor the large amount of force acts in shorter interval of time. So it hurts more.
(v) When the fielder pulls back his hands he experiences a smaller force for a longer interval of time leading to less damage to his hands.

40W. for the same applied voltage, power \(\alpha \frac{1}{resistance}\) If the power is less, higher will be its resistance.

(i) Torque is a vector quantity. It is acting along the direction which is perpendicular to the plane of action of force and distance.
(ii) Its SI unit is N m.
(iii) Examples : Turning a tap, winding or S unwinding a screw, spinning of a top etc.

It the molecular mass of a given substance is expressed in gram, it is known as gram molecular mass of that substance.

RBCs are biconcave and disc - shaped.

Electric power \(P=\frac { { V }^{ 2 } }{ R } \)
For the same value of V, R is inversely proportional to P.
Therefore, lesser the power, greater the resistance
Hence, the bulb with 40 W, 220 V rating has a greater resistance.

Rayleigh's scattering law states that "The amount of scattering of light is inversely proportional to the fourth power of its wavelength.
Amount of scattering \(\text { 's' } \propto \frac{1}{\lambda^{4}}\)

The reproductive period is marked by characteristic events repeated almost every month in physiologically normal woman (28 days with minor variation) in the form of a menstrual flow
The menstrual cycle consists of 4 phases:
(i) Menstrual or Destructive phase 
(ii) Follicular or Proliferative Phase
(iii) Ovulatory Phase
(iv) Luteal or Secretory Phase 

Mass of 1 mole of nitrogen \(\left(N_{2}\right)=2 \times N=2 \times 14=28 \mathrm{~g}\)
Mass of 3 moles of hydrogen \(\left(\mathrm{H}_{2}\right)=3[2 \times \mathrm{H}]\)
=3[2 x 1]=3[2]
=6 g
Mass of 2 moles of ammonia \(\left(\mathrm{NH}_{3}\right)=2\left[\mathrm{NH}_{3}\right]\)
=2[1 x N + 3 x H] 
=2[1 x14 + 3 x 1] 
=2[14 + 3] 
=2[17] = 34 g
\(\left.\begin{array}{c}1 \text { mole of nitrogen }(28 \mathrm{~g}) \\ + \\ 3 \text { mole of hydrogen }(6 \mathrm{~g})\end{array}\right\}=\text {2 moles of ammonia} (34 \mathrm{~g})\)

Based on the position of centromere, the chromosomes are classified as Telocentric, Acrocentric, Submetacentric andMetacentric.
(i) Telocentric - The centromere is found on the proximal end. They are rod shaped chromosomes.
(ii) Acrocentric - The centromere is found at the one end with a short arm and long arm. They are also rod - shaped chromosomes.
(iii) Submetacentric - The centromere is found near the centre of the chromosome. Thus forming two unequal arms. They are J

(iv) Metacentric - The centromere occurs in the centre of the chromosome and form two equal arms. They are V shaped chromosomes.

i) The digestive system includes the alimentary canal and the associated digestive glands.
ii) The alimentary canal consists of mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, caecum, large intestine and anus.
iii) Mouth leads to the buccal cavity.
iv) Through the pharynx it reaches oesopbagus.
v) Oesophagus opens into the stomach followed by smallintestine.
vi) Caecum ispresent in between the snnall intestine and large intestine.
vii) Caecunm contains bacteria that helps in the digestion of cellulose.
viii) Large intestine has colon and rectum.
ix) It finally opens in to the anus.
x) The digestive glands are salivary glands, gastric glands, liver, pancreas and intestinal glands. The secretion of digestive glands help in digestion of food in the alimentary canal.


 

(i) Corpus leuteum produces progestrone and its level increases followed by a decline if menstrual bleeding occurs.
(ii) Uterine wall ruptures bleeding starts and infertilized egg is expelled.

(i) The first fluid which is released from the mammary gland after child birth is called as colostrum.
(ii) Milk production from alveoli of mammary glands is stimulated by prolactin secreted from the anterior pituitary.
(iii) The ejection of milk is stimulated by posterior pituitary hormone oxytocin.

Leech is a parasite and sucks the blood of vertebrates and show adaptations.
(i) Suckers are present in the anterior and posterior ends of the body, by which the animal attaches itself to the body of the host.
(ii) The three jaws inside the mouth causes a triradiate or Y shaped wound in the skin of the host.
(iii) Saliva contains a protein called hirudin which prevents the blood clotting. Thus continuous supply of blood is maintained.
(iv) Blood is stored in the crop. It gives nourishment to the leech for several months. Hence, there is no digestive juices and enzyme.

Impulse = Change in momentum
P = 60 N ; t = 10 s
Change in momentum = Force x time
= 60 x 10
Change in momentum = 600 Ns