Question
What is sludge? Explain how it is treated.
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Answer
Semi-solids such as feaces that settle down during wastewater treatment are called sludge. This sludge is removed using a scraper and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas. This biogas is used as a low cost fuel for heating, cooking, etc. It is also used to produce electricity.
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(c) Dispersion$\quad$(d) Diffraction
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→Seema builds a periscope using plane mirrors and observes people behind a wall.
Q.1. The periscope works on the principle of:
(a) Refraction$\quad$(b) Reflection
(c) Dispersion$\quad$(d) Diffraction
Q.2. The number of mirrors required in a simple periscope is:
(a) 1$\quad$$\quad$(b) 2
(c) 3$\quad$$\quad$(d) 4
Q.3. Which angle do the mirrors make in a periscope?
(a) $45^{\circ}$$\quad$(b) $60^{\circ}$
(c) $90^{\circ}$$\quad$(d) $180^{\circ}$
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Fig. Experimental set-up
Fig. Experimental set-up