Simplify the following text for a Grade 7 native English-speaking person.
Original: On September 11 , 1820 , Ampere heard from the discovery of H.C. Orsted that a magnetic needle can be activated by a voltaic current .
Simplified: On 11 September 1820 he heard of H. C. Ã rsted 's discovery that a magnetic needle is acted on by a voltaic current .