Hi arul_prakasam,
Thank you for using the Apple Support Communities. Making sure your Mac operates as expected is definitely important. We see that your Mac is having some performance issues once the camera is activated, and we'll be happy to see how we can help out.
To verify, it sounds like you might have already checked Activity Monitor. Does a particular process showing the CPU usage there, or does it vary depending on the app you're using? View CPU activity in Activity Monitor on Mac
To troubleshoot this, we recommend two tests to help narrow things down. First, test in safe mode, which will help to rule out a few possible software causes: How to use safe mode on your Mac. Then click Apple menu () > Restart to get back to normal.
Second, we recommend creating a new administrator account and signing in there to see if you can replicate the issue, which will help work out if it's a system-wide or user-specific issue. Here's how to Set up users, guests, and groups on Mac.
Let us know the results of both tests.
Kind regards.