Yes. When you cast a spell you spend or fill the spellslot, but you do not lose the prepared spell. You can continue to cast it as long as you have equivalent spellslots to spend.
How many times can a wizard use a spell?
Note that it’s possible for a 1st level wizard to cast 2 spells per day of level 1 (see pp. 29); if he’s INT 18, he can have up to 5 prepared (INT 18 is a +4 modifier, and so level + Int Mod is 5). Likewise, a wizard of INT 9 or lower can prepare no spells at 1st level; he can only use his cantrips.
Can you cast multiple spells at the same time?
Yes, you can cast multiple spells at the same time and have both take effect. There are no rules against this. The rules are fairly clear about what is and is not allowed with regards to when and how spells can be cast.
Can a Wizard prepare more than one spell?
(An INT 8-9 Wizard can prepare a single spell at 2nd level; an INT 6-7 Wizard has to hit 3rd level to prepare one spell, but that spell can be a 1st or 2nd spell level. Also note that ritual use requires neither preparation nor a spell slot, so the idea of a low-Int Wizard isn’t the non-sequitur it may at first seem.
Can a Sorcerer cast more than one Cantrip in one round?
If the Sorcerer uses Quickened Spell to cast a cantrip as a bonus action, they may not cast a level 1-9 spell using their action (to prevent abuse of Quickened Spell being cheaper when used on cantrips). They may instead cast two cantrips (action & bonus) in this way.
Can a bonus action spell be cast in the same turn?
Note that this will not work with bonus action spells because the restriction on those means that only 1 action cantrips can be cast the same turn. Simultaneously, No. In the same turn, Yes. Sage Advice has already addressed the issue of casting multiple spells in the same turn, which is very much RAW.
