question
5.20(a). a compass needle free to turn in a horizontal plane is placed at the centre of circular coil of 30 turns and radius 12 cm. the coil is in a vertical plane making an angle of  with the magnetic meridian. when the current in the coil is 0.35 a, the needle points west to east.  determine the horizontal component of the earth’s magnetic field at the location.
318
(a) clockwise would be the direction of magnetic field in wire a.(b) the direction of the magnetic field in the wire b is anticlockwise.maxwell’s right hand thumb rule. that depends on a lot of things. in particular, you would need to find the electric susceptibility of the paper. the field produced by static charge is inverse-square. the polarization of the paper varies directly with the external field, with a proportionality constant equal to the electric susceptibility. the dipole field created by the polarized paper is inverse-cube. overall, the force between the ruler and the paper will vary with the inverse fifth power of distance. to get any more detailed, you would need to know the geometry of the situation, and the charge distribution. 圖片參考：http://imgcld.yimg.com/8/n/ab00135862/o/161006040753513872668990.jpg
 
首先請先 複習下列公式
 
設扇形的中心角θ弳，半徑為r，弧長為s，面積為a，則
s=rθ；a= r2θ= rs
sol: 設: ∠aob=θ 弳 (弧度) od=x
(x+2.5) θ =6 ……………………………..(1)
求黃色部分面積= (x+5)2 θ - x2θ
= θ ( x2+10x+25-x2 )
= θ (10x+25)
=5θ( x + 2.5)=30



圖片參考：http://imgcld.yimg.com/8/n/ab00135862/o/161006040753513872669011.jpg
 

圖片參考：http://imgcld.yimg.com/8/n/ab00135862/o/161006040753513872669012.jpg
 

圖片參考：http://imgcld.yimg.com/8/n/ab00135862/o/161006040753513872669033.jpg
 



 2010-06-04 23:25:06 補充：
y= |cosx|

恕不再多畫 將以文字說明

1. 當cosx >0 時 y=cosx
2. 當cosx <0 時 y = -cosx

 2010-06-04 23:26:21 補充：
注意

y=3sin2(x-π)+2

之 a , b 步驟為同一圖形

 2010-06-05 13:06:49 補充：
奇怪 1/2 通通不見了

更正

s=rθ；a=0.5 r2θ=0.5 rs

求黃色部分面積=0.5(x+5)2 θ - 0.5x2 θ
=0.5θ ( x2+10x+25-x2 )
=θ (10x+25)
=5θ( x + 2.5)=30

p.s. x2 即為 x平方

 2010-08-28 11:35:07 補充：
staff
crusty
dough
yeast
ferment
form
trap
raise
rise
flat
slab
acorn
slope
pound
protein
wheat
rye
grind
coarse
gluten
elastic
expand
carbon
dioxide
technique
wear away
grit
swiss
crush
steel
roller
rid of answer: eddy currents are currents that circulate in conductors like swirling eddies in a stream. they are induced by changing magnetic fields and flow in closed loops, perpendicular to the plane of the magnetic field. they arise when a conductor moves through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying. to summarise, we can say that anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field produces eddy currents. the two uses of eddy current are: it is used in household current meters to measure power consumption. it is used to check whether the material or surface has any discontinuities, fractures, or faults without harming the material. what are the functions of a transformer? what is the working principle of a transformer? the force on the wire due to the interaction of magnetic fields of the bar magnet and current carrying wire can act only in upwards or downwards direction. let c1 and c2 are two concentric circles with center o and radius of outer circle is 5 cm.given : ac is a chord with length 8 cm that is tangent to inner circle .to find : radius of inner circle i.e. odac is a tangent for c1 at d so,od ⏊ ac [tangent at a point on the circle is perpendicular to the radius through point of contact ]so, oad is a right-angled triangle at d .also it implies that od is perpendicular to the chord ac in c2so we have,ad = dc [perpendicular from the center to the chord bisects the chord]ac = ad + dc8 = ad + adad = 4 cmin △oad by pythagoras theorem(oa)2 = (od)2 + (ad)2(5)2 = (od)2+ (4)225 = (od)2 + 16(od)2= 9od = 3 cm All that is needed is some sort of wave-shape that sweeps the oscilloscope beam to and fro. Since the relationship between vertical displacement and horizontal displacement on the oscilloscope’s trace is purely a function of the test component’s characteristic curve, we really don’t care what form of [AC](https://www.allaboutcircuits.com/textbook/alternating-current/chpt-1/what-is-alternating-current-ac/) voltage excites it. net work done in carrying charge along closed loop by electric field is zero. hence, the tangential component of the electric field is continuous from one side of a charged surface to the other. let a and b be the two given vectorsɵ = 150° is the angle between a and bif c is the resultant vector, then: ...1also, it is given that the resultant is perpendicular to one of the given vectors. let that given vector be anow, …2putting 2 in 1, we get:now, putting c = 10, ɵ = 150° ()so, hence, smaller vector is a = 20 units fleming’s right hand rule is used to find the direction of the?