(2) The trajectory of charge is shown in the figure. There is a uniform magnetic field in the fourth quadrant, and the charge moves in a uniform circle, which is obtained by Newton's second law:
qvB=mv2R,
According to the knowledge of geometry, θ = 45× 2 = 90,
2Rcos45 =。 OP=2,
Solution: R= 1m, b = 0.02t t.
The charge moves at a uniform speed in the electric field, which is obtained by Newton's second law: a=qEm,
According to the speed formula of uniform variable speed motion, 0=v0-at2,
Simultaneous and alternative data: e = 200 n/c;
(3) The position where the charge passes through the X axis for the third time: X = XP+2COS = 22m;;
(4) After passing through the X axis for the third time, the charge moves like a flat throw, and the initial velocity direction is R=v0t.
Direction of electric field force: R= 12a2t22,
According to Newton's second law: a2=qE'm,
Simultaneous and alternative data: e ′ =1.6×104n/c;
Answer: (1) The charge is negatively charged, and there is a uniform electric field in the first quadrant. Direction: the positive direction of the X axis is inclined upward by 45;
(2) The magnetic induction intensity is 0.02T, and the electric field intensity is 200 n/c;
(3) The position where the charge passes through the X axis for the third time is 22m;;
(4) The changed electric field intensity is1.6×104 N/c. 。