# Thread: define given parameter of direct current electricity and magnetic fields

1. ## define given parameter of direct current electricity and magnetic fields

1) whats the eqaution which defines the CURRENT flow in an electrical circuit in terms of CHARGE & TIME?

is it Q/IxT or I/QXT?

2) whats the equation which defines the RESISTANCE of a circuit in terms of CURRENT & POTENTIAL DIFFERENCE?

is it P/IxV or V/IxR?

3) car headlap takes a CURRENT of 450mA. how much CHARGE passed through the lamp when using during a 40min journey at night?

is it 0.45 A? x 40 mins? =

2. Originally Posted by turbod15b
1) whats the eqaution which defines the CURRENT flow in an electrical circuit in terms of CHARGE & TIME?

is it Q/IxT or I/QXT?

2) whats the equation which defines the RESISTANCE of a circuit in terms of CURRENT & POTENTIAL DIFFERENCE?

is it P/IxV or V/IxR?

3) car headlap takes a CURRENT of 450mA. how much CHARGE passed through the lamp when using during a 40min journey at night?

is it 0.45 A? x 40 mins? =

1) Current is defined as $\displaystyle I = \frac{Q}{t}$ or if you have a Calculus based class $\displaystyle I = \frac{dQ}{dt}$.

2) I'm not sure of the problem here. Perhaps you are confusing the symbol for power, P, with the symbol for potential difference, V. (Many students get this mixed up at one point or another.) In any case you are looking for an equation for R in terms of I and V. Ohm's Law states that $\displaystyle V = IR$ so $\displaystyle R = \frac{V}{I}$

3) From the first problem we know that
$\displaystyle I = \frac{Q}{t}$

$\displaystyle Q = It = (450 \, mA)(40 \, min) = \left ( \frac{450 \, mA}{1} \cdot \frac{1 \, A}{1000 \, mA} \right )$ $\displaystyle \left ( \frac{40 \, min}{1} \cdot \frac{60 \, s}{1 \, min} \right )$

$\displaystyle Q = 1080 \, C$

-Dan

3. thank u