Changes Around Us: Physical and Chemical — Science STD 7 — Question

For setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting if the temperature of the mixture remains approximately between 35°C to 40°C. At places, where room temperature remains much below the range, setting of curd becomes difficult. Suggest a way to set curd in such a situation.

Show the shape of the distance-time graph for the motion in the following cases
(a) A car moving with a constant speed.
(b) A car parked on a road side.

What will happen if there are no platelets in the blood?

A student covered a torch with red cellophane sheet to obtain red light. Using the red light she obtains a shadow of an opaque object. She repeats this activity with green and blue light. Will the colour of the light affect the Shadow? Explain.

Identify and compare breathing organs in fish, frogs, and humans using a chart.

Draw a labelled diagram of human respiratory system.

How does a periscope help us see things not in direct line of sight?

A train travels 180 km in 3 h. Find its speed in:
(i) km/h
(ii) m/s
(iii) What distance will it travel in 4h if it maintains the same speed throughout the journey?

What happens when a candle is burnt? Explain the physical and chemical changes involved.

Explain the working of an electric switch in a circuit.