If you play a wrong ball, you incur a 2-stroke penalty.
See Rule: 6.3c.

You will find this and more than 2,000 other quiz questions about golf rules on six levels in the learning app GolfQuis. 

Knowing the rules will give you more options when playing a round of golf – and often, you will be able to save a stroke or more. However, many of us find it difficult, time-consuming, or just plain boring to learn the rules by reading books or attending courses.

GolfQuis is an app that helps you learn the rules in a way most golfers find motivating – some, even fun. The picture shows one of the more than 2,000 rules questions from the quiz. 

Try GolfQuis for free
A free trial is available on the Apple App Store and Google Play. Why not try it? You only risk getting better at the rules of golf. If you decide to move on with the full version, the price is around the same as two new golf balls.