Laravel eloquent relationship query does not work

I would like to get all quizzes with the topics which have a course_id:

The Topic model has the following function:

public function quizzes()
{
    return $this->hasMany('App\Quiz');
}

The Quizzes model has the following function:

public function topic()
{
    return $this->belongsTo('App\Topic', 'topic_id');
}

This is the code in my controller function:

$topics = Topic::with('quizzes')->whereCourseId($course_id)->orderBy('created_at', 'asc')->get();

return dd($topics->quizzes);

I get the following Exception error:

Property [quizzes] does not exist on this collection instance.

I seem not to know whats happening?

via Chebli Mohamed