Question

give reasons for why Shimla is colder than Ludhiana

Answer 1

Its simple physics. Ludhiana is practically at sea level while shimla is at 2200m. We know that as we move higher, the pressure decreases. So while pressure exerted by air molecules  at sea level(ludhiana) is 14.7psi it will be around 12-13 psi in shimla which is at higher elevation. We know that when we compress a gas, its temperature rises and when we let it expand, its temperature must fall. So beacuse of lower pressure exerted by atmospheric air in shimla, its temperature will almost always be lower than ludhiana.
other effects similar to what I explained
1) release the air from your car tyres, It will be cold air coming out as the air is moving to an area of low pressure and its temperature will reduce in the process.
2)joule-thomson effect- For almost all gases when released from an area of higher pressure to an area of lower pressure, cooling is observed.
3) In a refrigerator/AC the condesed refrigerant is at normal temperature usually 30-40 deg but when expanded its cools down significantly and hence we get the refrigerant effect. This is how you achieve the 20deg temp you maintain in your car or the 5deg C you maintain in your refrigerator

Answer 2

shimla is a place in higher altitudes and the as the altitudes are increasing the temperature starts to decrease and ludhiana is located in small altitudes area that's why shimla is colder than ludhiana