Electricity: Magnetic and Heating Effects — Science STD 8 — Question

Human male gamete has a tail but female gamete does not. Why?

A group of students is experimenting. They have two beakers, A and B, each containing 100 mL of water. In beaker A, they add 5 grams of salt and stir. In beaker B, they add 20 grams of salt and stir. They observe that all the salt in beaker A dissolves, but in beaker B, some salt remains at the bottom, even after stirring vigorously.
Q.1. Why did all the salt dissolve in beaker A, but not in beaker B?
Q.2. What kind of solution is formed in beaker A?
Q.3. What about beaker B (considering the undissolved salt)?

Riya is preparing lemonade for her friends on a hot summer day. She takes a jug of water, adds some sugar, and stirs it well. Then, she squeezes some lemons into the jug and mixes everything. She notices that the sugar completely disappears, but the lemon pulp settles down a bit after some time.
Q.1. In Riya’s lemonade, identify the solute(s) and the solvent.
Q.2. Why did the sugar dissolve completely in the water, but the lemon pulp settled down?
Q.3. If Riya wants the sugar to dissolve faster, what could she do?

Comment on dilute solution and concentrated solution. Which of them gives the solubility of the solute? Explain.

Describe the threat to Taj Mahal monument due to air pollution.

How will you find out whether an object is charged or not?

Explain how burning of fuels such as coal, petrol and diesel leads to acid rain. Give the harmful effects of acid rain.

Abida and Ramesh want to heat water taken in separate beakers. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time? Why?

There are two boxes, one made of metal and the other made of wood, which are similar in appearance. How will you find out which box is made of metal?