Read the article Looking at Leaves and answer the question. What causes leaves to change color in the autumn? Is the change physical or chemical? Explain your answer.

Both chemical and physical change

Explanation:

Physically, the change in color is due to the addition and subtraction of pigments such as chlorophyll, carotenoids and anthocyanins

Chemically, the change results from the conversion of the pigments chemicals such as chlorophyll and anthocyanins product one form to another product.

From the article, it is noted that during the autumn, there is cooler weather and less sunshine due to shorter days, and hence the trees instead of relying on the sunshine for the production of plant food through photosynthesis, the trees absorbs the food stored in the leaf for storage and nutrition during the winter periods, in the process, chlorophyll, the substance that gives the leaves their green color, is broken down and the leaves changes color.

After the chlorophyll is broken down other chemicals present carotenoids and anthocyanins (formed by trapped sugar in leaves) provide pigments which gives the leave.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.