The nervous system controls and coordinates all the functions in the body. It carries out its function in close coordination with hormonal system. Nerves don’t reach every hook and comer of body, hence needs assistance from hormones to control all the parts of body. Nervous control is faster. Hormonal control is slower. Hormonal control is based on feedback mechansim and tells body to pace up or slow down. Nervous control is on other hand a direct control. So we can say that both system work in harmony.
<p>When bright light is focussed on our eyes it goes to the brain, the brain reverts back the message by motor neuron which contracts the pupil. The sequence of events which occur is as follows:</p>
The green plants are called autotrophes. They make their own food by the process of photosynthesis. In this process the plants capture the sun rays by the pigment present in the leave called as chlorophyll. Then in the presence of carbondioxide and water they make food for the plants in the form of glucose. In this process oxygen gas is also evolved. Equation for the mechanism: <img alt="" src=" " />
<p>Mendel used pea plant (Pisum sativum) when he crossed tall and short plants the progeny obtained in FI generation were tall. When the F1 plants were selfed the F2 generations showed three tall and one dwarf plant. The genotypic ratio of F2 generation is 1 : 2 : 1 (TT : Tt : Tt : tt)<br /> The phenotypic ratio is 3 : 1 (Tall : Dwarf)</p>
2AgCl → 2 Ag + Cl₂ Initially, the colour of silver chloride is white but when it is kept in sunlight it breaks down to give silver and chlorine. Hence, the colour changes to grey. It is an example of Photo-Chemical Decomposition reaction.
(i) Sodium is a group one element (Na) so its configuration is 2, 8, 1 and its valency is 1. Oxide has a valency of 2. So its formula would be Na₂O. Similarly, formula of X element of the first group would be X₂O.
Halide is any Halogen. Halogen has valency of 1. Group 13 elements have valency of 3. SO, The formula of halide(Y) of X element of group thirteen would be XY₃. For example, we take Aluminium (Al) its configuration is 2, 8, 3, the valency of Al is 3, the valency of Cl is 1 So, Formula would be AlCl₃ (Aluminium chloride).
Element of group 2(X²⁺) have valency of 2 and element of group 17(Y⁻) have valency of 1. Formula of these elements would be XY₂. Element of group 2, for example, Mg 2, 8, 2 its valency would be 2. Element of group 17 would be Cl 2, 8, 7 valency would be 1. Formula would be MgCl₂ (Magnesiun Chloride)
1. Sodium chloride is an ionic compound but it conducts electricity only in molten and aqueous state because in molten and aqueous form the compound liberate to give ions. These ions move freely and hence conduct electricity. 2. Reactivity of aluminium decreases if it is dipped in nitric acid because it is a strong oxidising reagent. The layer of aluminium oxide prevents further reaction of aluminium due to which its reactivity decreases. 3. Metals like calcium and magnesium are never found in their free states in nature because these metals are present on the top of the reactivity series. They are so reactive that they react with gases and surrounding elements, form compounds and thus are not found in free state.
"<img alt="""" src="" "" /> Consider three resistors R₁, R₂, R₃ connected in parallel with a battery as shown in the figure. The potential difference across each of the resistor is same as the applied voltage, but the value of current across each resistor is different. Let I₁, I₂, I₃ be the current through R₁, R₂, R₃ respectively. ∴ I = I₁ + I₂ + I₃ .........(i) Let the effective resistance of this parallel combination be RP then using Ohm's Law I = V/Rₚ ............(ii) As V is same for all resistor therefore I₁ = V/R₁, I₂ = V/R₂, I₃ = V/R₃ ………(iii) Hence, from equation (i) , (ii) and (iii) we get V/Rₚ = V/R₁ + V/R₂ + V/R₃ ⇒1/Rₚ = 1/R₁ + 1/R₂ + 1/R₃ i.e., the reciprocal of effective resistance in parallel combination is equal to the sum of reciprocals of all the individual resistances."
