# What does this - ^ mean when it is over a value?

1. May 29, 2010

### mapa

What does this -- "^" mean when it is over a value?

The equation for an electric field is E = 1/4pie(epsilon) * Q/r^2 *(^r" I do not know how to put the roof over the r so i put it right next to it")

What does this value mean because I have also seen it occur with distance. It seems to me like it does nothing for the final answer. What does it do?

2. May 29, 2010

### Hurkyl

Staff Emeritus
Re: What does this -- "^" mean when it is over a value?

The hat is a kind of decoration to put on symbols -- it's just another way to vary a symbol, like varying the font or the case or the language.

One common use for the hat is to indicate the variable represents a unit vector, specifically the normalization of the ordinary vector represented by the same base letter.

3. May 29, 2010

### D H

Staff Emeritus
Re: What does this -- "^" mean when it is over a value?

$$\mathbf E = \frac 1 {4\pi\epsilon_0}\,\frac Q{r^2}\hat{\mathbf r}$$

The electric field is a vector field rather than a scalar field. All of the terms on the right hand side except the final $\hat{\mathbf r}$ are scalars. That final $\hat{\mathbf r}$ is a unit vector that points away from the central charge.