Lightning caused by an electric discharge from a negatively-charged cloud to a positively charged ground is often accompanied by another bolt of lightning in the reverse direction. This is called a 'return stroke and it travels from the Earth to the cloud. Discuss why and how a return stroke is caused.

Explanation

### Step-by-Step Text Solution:

1. **Understanding Lightning**: Lightning is a natural phenomenon that occurs due to the discharge of electricity in the atmosphere. It typically happens between a negatively charged cloud and the positively charged ground.

2. **Formation of Charge**: During a thunderstorm, the movement of air causes the separation of charges within the cloud. The upper part of the cloud becomes positively charged, while the lower part becomes negatively charged. The ground beneath the cloud also becomes positively charged due to the influence of the negatively charged cloud.

3. **Initial Discharge**: When the electric potential difference between the negatively charged cloud and the positively charged ground becomes large enough, a discharge occurs in the form of a lightning bolt. This is the initial lightning strike that travels from the cloud to the ground.

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