List two advantages of using biogas over fossil fuels.

Vidushi had learnt about the principle of conservation of energy. One day, she was required to write an essay on the topic-Energy crisis and its possible solutions. This perplexed her. So, she asked her teacher how could there be a crisis of energy when the total energy of the universe is constant. Her science teacher politely explained the reason to her.

What is meant by 'energy crisis'?

Vidushi had learnt about the principle of conservation of energy. One day, she was required to write an essay on the topic-Energy crisis and its possible solutions. This perplexed her. So, she asked her teacher how could there be a crisis of energy when the total energy of the universe is constant. Her science teacher politely explained the reason to her.

What characteristics were exhibited by Vidushi?

Three incandescent bulbs of $100 \mathrm{V}$ each are connected in series in an electric circuit. In another circuit wattage set of three bulbs of the same voltage are connected in parallel to the same source.

Will the bulb in the two circuits glow with the same brightness? Justify your answer.

Three incandescent bulbs of $100 \mathrm{V}$ each are connected in series in an electric circuit. In another circuit wattage set of three bulbs of the same voltage are connected in parallel to the same source.

Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.

A student focuses the image of a candle flame placed at about $2 \mathrm{m}$ from a convex lens of focal length $10 \mathrm{cm}$ on a screen. After that, he gradually moves the flame towards the lens and each time focuses its image on the screen.

In which direction does he move the lens to focus the flame on the screen?

A student focuses the image of a candle flame placed at about $2 \mathrm{m}$ from a convex lens of focal length $10 \mathrm{cm}$ on a screen. After that he gradually moves the flame towards the lens and each time focuses its image on the screen.

What happens to the size of the image of the flame formed on the screen.

A student focuses the image of a candle flame placed at about $2 \mathrm{m}$ from a convex lens of focal length $10 \mathrm{cm}$ on a screen. After that he gradually moves the flame towards the lens and each time focuses its image on the screen.

What difference is seen in the intensity (brightness) of the image of the flame on the screen?