Question

IV. Answer the following questions:
9x3=27
25. The Magnetic field associated with a current carrying straight conductor is
in anticlockwise direction. If the conductor was held along the east-west
direction. What will be the direction of current through it? Name and state
the rule applied to determine the direction of current?
OR
What is short circuting? State one factor that can lead to it. Name the device
in the household that acts as a safety measure for it. State the principle of its
working
26. Explain how harmful chemicals enter our body.
27. Biomass contains stored energy. Justify. How does bio-gas plant help to reduce
the problem of pollution.
OR
Mention why is it not possible to make use of solar cells to meet our energy
needs? State three reasons to support your answer.
28. A white coloured powder used by doctors for supporting factured bones
i) Write chemical name and molecular formula of the powder.
ii) When this white powder is mixed with water a hard solid mass i
obtained. Write balanced chemical equation for the change.
OR
a) What is the role of tooth pastes in preventing cavities?​

Answer 1

Explanation:

25. The direction of current will be towards west

The Right-Hand Thumb Rule is used here which states that 'If a current-carrying wire is held in the right hand such that the thumb points to the direction of the current, then the curl of fingers will give the direction of magnetic field'.

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26. Since plants are at the primary level of the food chain, they are the main source of energy. Farmers use pesticides and insecticides to facilitate their growth. Due to this, the secondary consumer, mainly insects,herbivores,etc., consume these harmful chemicals.

Furthermore, the pesticides are non-biodegradable and do not decompose in the bodies.So, they start to accumulate in the bodies of organisms belonging to each successive trophic level. Since humans are at the top of food chain, they contain the maximum concentration of these harmful chemicals. Such process of accumulation is called Biological Magnification.

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27. It is not possible to make use of solar cells to meet our energy needs because of the following reason:-

1. Construction of solar cells is very expensive, silver used for interconnecting cells adds to the cost.
2. It cannot be used in cold and temperate areas as the main principle is to absorb heat by sunlight and the amount of sun rays reaching the areas is not sufficient.
3. Special grade silicon, used for making solar cells. is limited.

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28.

1. The chemical name of the white powder is Calcium Sulphate Hemihydrate. The common name is Plaster of Paris. Its molecular formula is CaSO4 .1/2H2O
2. When it is mixed with water, it turns into gypsum, a hard solid substance. The following is the chemical reaction involved

CaSO4. 1/2H2O +3/2H2O = CaSO4 + 2H2O