Can electric field be negative? - Physics Stack Exchange most recent 30 from physics.stackexchange.com 2019-09-15T12:16:30Z https://physics.stackexchange.com/feeds/question/390461 https://creativecommons.org/licenses/by-sa/4.0/rdf https://physics.stackexchange.com/q/390461 1 Can electric field be negative? susan J https://physics.stackexchange.com/users/181194 2018-03-06T11:22:41Z 2019-06-08T03:13:24Z <p>According to the equation , $$E = kQ/r^2$$</p> <p>If the source charge is negative electric field produced by the charge must also be negative. My teacher said electric field can never be negative, it'll either be <strong>positive or zero</strong>. Online sources pointed out that since electric field is a vector when doing calculation we only report the magnitude.</p> <p>Another doubt was with electrostatic force is,why is it always positive? According to columb's law force is directly proportional to modulus of product of charges. Can't it be negative like attractive and repulsive forces.</p> https://physics.stackexchange.com/questions/390461/-/390465#390465 1 Answer by jim for Can electric field be negative? jim https://physics.stackexchange.com/users/109388 2018-03-06T11:42:59Z 2018-03-06T11:42:59Z <p>The electric field is a vector quantity. For the vector ${\bf v}$ you can write this as $|{\bf v}|$ multiplied by a unit vector, say ${\bf n}$, that is $${\bf v} = |\bf{ v}| {\bf n}.$$</p> <p>It is conventional to take the magnitude as a positive number, but if you take it as a negative number you can write $${\bf v} = -|\bf{ v}| (-{\bf n})$$ and the field points in the opposite direction. </p> https://physics.stackexchange.com/questions/390461/-/390471#390471 1 Answer by Steeven for Can electric field be negative? Steeven https://physics.stackexchange.com/users/4962 2018-03-06T12:12:58Z 2018-03-06T12:12:58Z <p>Try to ask yourself the question: what does it mean that <em>anything</em> is "negative"? The term "negative" has no physical meaning in itself before we define it to mean something. </p> <ul> <li><p>How does a <em>negative number</em> (scalar) make physical sense? What does $-2\;\mathrm{kg}$ or $-10\;\mathrm{apples}$ mean? We can choose to understand it as the <em>loss</em> of an amount when it fits the context. </p></li> <li><p>How does a <em>negative arrow</em> (vector) make physical sense? What does $-\vec F$ or $-\vec v$ or $-\vec E$ mean? We can choose to define it as <em>the opposite</em> of the vector, meaning the same vector in the opposite direction. </p></li> </ul> <p>And so, a negative vector - or more precisely: <em>the negative of a vector</em> - has been defined to mean: The same vector in the opposite direction.</p> <p>Now that we have a chosen definition, we can use any vector quantity with signs. Forces, velocities and also fields, including electric fields, are represented by vectors. A negative electric field just means: <strong>a field pointing/pushing opposite to what a positive field would do.</strong></p> https://physics.stackexchange.com/questions/390461/-/484893#484893 0 Answer by Arshdeep Singh for Can electric field be negative? Arshdeep Singh https://physics.stackexchange.com/users/234060 2019-06-08T03:13:24Z 2019-06-08T03:13:24Z <p>Electric Field can never be negative . As electric field is Force experienced by charge divided by magnitude of charge . So in magnitude , we take mod of charge. So even in case if charge is negative , then due to mod it becomes positive . Hence Electric Field also becomes positive . So , electric field is always positive . </p>