When we expose half of a nail outside on a sunnyday then we cover the other half with cartoon the cove red half still gets heated why is this so?

When half of a nail is exposed to sunlight, it absorbs heat from the sun directly. The covered half, even though it’s shielded by cardboard, can still absorb heat through conduction from the exposed portion, which is transferring heat to the rest of the nail. Additionally, the cardboard may not be a perfect insulator, allowing some heat to reach the covered side. Thus, both halves of the nail can become warm even if only one side is directly exposed to sunlight.