The wands do not repel each other in this scene. It appears that way because the Death Eaters are using non-verbal spells to try and disarm Harry and his friends. They are casting spells without incantations, making them seem more powerful and instantaneous.
The way it appears that the wands are repelling each other is likely due to the rapidly cast spells and the intense light and sound effects used in the film.
Here's a breakdown of why it seems that way:
* Non-verbal spells: The Death Eaters use magic silently, making it seem like their wands are firing off spells at a much faster rate than Harry's, which is still accompanied by incantations.
* Visual effects: The film utilizes special effects to show the spells clashing and deflecting, creating the illusion of repulsion.
* Editing: The editing in the scene cuts quickly between the different spells, making the action feel more chaotic and impactful.
However, there is no specific magic or phenomenon that makes wands repel each other. The scene is intended to create a thrilling action sequence and emphasize the danger and intensity of the chase.