No sound when connecting additional DELL screen by HDMI to DELL Inspiron 15 5000

i have just purchased a DELL Inspiron 15 5000 SERIES - 5559 with Windows 10 Pro pre-installed in Spanish. I have also purchased a DELL 24" additional screen SE2416H.

Whilst watching live internet broadcasts (TV, Youtube etc.) on Chrome, Edge or Firefox, as soon as I connect the screen to the laptop by HDMI cable, the sound on my laptop speakers disappears. Upon disconnection of the HDMI screen cable, the sound re-appears.  

However, the sound doesn't disappear when using other sound applications such as Skype. 

This means I can't enjoy watching internet TV with sound on the 24" screen.

Please advise how to fix this as the main point of purchasing the 24" screen was precisely to be able to watch (and listen to) TV programs.

Regards,