You know two directions and you need the third. One convention everywhere on this page: +x is right across the screen, +y is up it, +z is out of the page toward you, so into the page is −z. A circle with a dot means out of the page; a circle with a cross means into the page. All three rules use conventional current, which runs opposite to the electron drift. Arrow lengths on the canvas are indicative, not to scale, and the trainer covers only the six axis directions.
v x B: right x out of page = down
I x r: right x up = out of page
sense: anticlockwise from the right end
Velocity v pointsright
Field B pointsout of page
Charge signpositive
Charge size1 e
Speed v3.0e6 m/s
Field B0.40 T
Force direction F = q v x B
down (-y)
Force magnitude
1.923e-13 N
Angle from v to B
90 deg
Charge q
+1 e
q v B sin(angle)
1.923e-13 N
Current I runsright
From the wire, you goup
Current I10.0 A
Distance r0.050 m
Field direction where you stand B along I x r
out of the page (+z)
Field magnitude B = µ0 I / 2πr
40.00 µT
Distance from the wire
0.050 m
Current I
10.0 A
B at twice that distance
20.00 µT
Current senseanticlockwise
Current I2.0 A
Turns per metre n1000 /m
North end curl the fingers with I
right end (+x)
Field inside B = µ0 n I
2.5133 mT
Turns per metre
1000 /m
Current I
2.0 A
South end
left end (-x)
µ0 = 4π × 10^-7 T·m/A — measured since the 2019 SI redefinition, right to two parts in 10 billion · e = 1.602176634 × 10^-19 C · the force comes from the cross product, never from q v B sin(angle); the check card shows what that sine form returns instead.