I have a 14" Laptop with an Intel HD 4000 and nVidia GT 620m, I was wondering if I used an external monitor, would it stress the GPU's since the external screen is twice as big? I bought a laptop and the screen was smaller than expected so I wanted to use an external monitor but wasn't sure if it would put any stress on the GPU since the screens were bigger. Does anyone know if using a bigger screen affects the GPU in a bad way?
If the bigger screen has a bigger resolution, your GPU will have more work to do in order to display the same image. Using the external screen alongside your laptop screen (not turning laptop screen off) causes your GPU to render two images instead of one, which is even more work.
However, none of this is bad for your GPU. Your GPU was most likely designed to support a dual monitor setup. There would not be a connector for your external monitor otherwise. It can be the case that while using the external monitor or both monitors your performance will be lower, especially while playing games. It should however still be good enough for normal day-to-day use and is not harmful for your GPU.
Should your GPU really push the limits and stress itself, it will become hotter. There is a safety mechanism in place that will automatically shut down your laptop when the temperature becomes too hot in order to prevent any damage.
Judging your situation specifically, I think you can hook up an external monitor just fine and you won't even notice a performance decrease.