26 Replies
I'm all confused here
Here's what I assumed:
Propagation vector is 3i + 4j from inside the bracket (c vector)
Electric field vector is 4i - 3j (E vector)
Doing c vec = E vec cross B vec (after assigning
B = <p,q,r>) gives r = -1 and 4q=3p
And if r = -1, it should be -k cap
I didn't think that way in the exam, I just saw the magnitude of the E vector was = 5 so I marked the 5kcap option
Which was somehow closer to the original answer
🤷 I'm lost@Gyro Gearloose
Yea, your method is correct and that gives -5 k cap no?
._.
lemme check again
ExB=(4i-3j)x(-5k cap)=20j+15i which is in direction of 3i+4j
c vec=E vec cross B vec is kinda wrong no you have to compare only their direction vectors and then c=EB for the magnitue
ok nvm, in my method i'm getting (4q+3p) kcap where q and p are unknown constants
how'd you get from there to -5
magnitude toh i got, anyway 57/3*10^8 is the magnitude of all the options
We have E=4i-3j and c=3i+4j so B must be along the z-axis. Now, either you can see by the right hand rule or just compare from options.
all the options are along z-axis
Yeah but use right-hand rule no? It gives you B is along -z axis.
wait shouldnt the ans be C then
And magnitude we know to be 5 ig.
oh okay yeah i can use right hand rule on 3x+4y and 4i-3j
how
same question
okay -z part i got
Actually write the E-field as 5(number infront of given E-field) so as to get the unit vector for E.
Now, the magnitude of B field is (5number infront of E-field)/c
Direction of B-field is -k
So now just write it as (number infront of E-field/c)*(-5k)
oh shit wait
some of the magnitude of the electric field is contained in the 4i - 3j
that's the part i was missing and the spidey sense i had in the exam
i.e. the magnitude of Efield is 5*57, not 57, since the magnitude of 4i - 3j is = 5
@hithav
lance is this correct
yeah
Yep.
thank god i went briefly insane over this
bhery nice ques
+solved SirLancelotDuLac
oup
💀 we need to up our level if we think this is a bhery nice ques
naw naw its all good i learnt something
thats all that matters
now i hope a similar ques comes in mains and ppl get confused
same >:)
+solved @SirLancelotDuLac
Post locked and archived successfully!
Archived by
<@852788017243357194> (852788017243357194)
Time
<t:1743093032:R>
Solved by
<@1075951732460376214> (1075951732460376214)