SolveItClass 9 · NCERT

NCERT Solutions · Class 9 Science Earth as a System: Energy, Matter, and Life

23 questions · 23 still being checked

Pause and Ponder 13.1–13.2 (part 2 of 11)

  1. Exercise 13.1

    Visit the website given below and study the effect of the concentration of greenhouse gas on surface temperature, https://phet.colorado. edu/en/simulations/ greenhouse-effect 258\displaystyle 258 Exploration|Grade 9\displaystyle 9

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    The simulation shows that surface temperature rises as the greenhouse gas concentration is raised — more gas, warmer surface.
    NCERT_Solution_Class9_Science_Ch13_PP_Q13-1
    Set the concentration slider to a low value: most of the infrared radiated by the ground escapes to space, and the thermometer settles at a low reading.
    Slide the concentration up: more infrared is absorbed by the gas and sent back down, the ground receives extra energy, and the thermometer reading climbs.
    Compare the built-in presets (ice age / pre-industrial / today): the same Sun gives a colder Earth when the greenhouse gas level is lower.
    This is exactly the chapter's mechanism — the surface absorbs sunlight and re-radiates it as infrared, and \(\displaystyle CO_{2} \), \(\displaystyle CH_{4} \) and water vapour trap part of that outgoing heat.
    Take-away: some greenhouse gas is essential (without it the Earth would be too cold for life), but excess drives global warming.

  2. Exercise 13.2

    How does the cool mountain breeze benefit agriculture activity, particularly the crops and soil?

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    The cool mountain breeze lowers the night temperature in the valley and slows moisture loss, which helps both the crop and the soil.
    NCERT_Solution_Class9_Science_Ch13_PP_Q13-2
    After sunset the mountain slopes lose heat faster than the valley floor; the air above them becomes cool and dense and drains down into the valley as a steady night wind over the fields.
    Cooler nights mean less evaporation from the soil and less transpiration from leaves, so the soil holds its moisture longer and needs less irrigation.
    The cool, moist air favours dew formation, adding a little extra water to the leaves and the topsoil.
    Cool nights relieve the day's heat stress on plants; the large day–night temperature swing this creates is what many hill crops (apple, tea, potato) need for good quality.
    By regulating temperature and moisture conditions in this way, mountain breezes support soil and crop health in hilly regions like Shimla and Dehradun.