国外物理题（概念）,关于声波的We cannot see a sound wave.However we can see a representation of it by connecting a microphone to————————(b) The pitch of a sound depends on——————————(c) The loudness of
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国外物理题（概念）,关于声波的We cannot see a sound wave.However we can see a representation of it by connecting a microphone to————————(b) The pitch of a sound depends on——————————(c) The loudness of
国外物理题（概念）,关于声波的
We cannot see a sound wave.However we can see a representation of it by connecting a microphone to————————
(b) The pitch of a sound depends on——————————
(c) The loudness of a sound depends on————————————
第二个问题哈：
A wire carries a current.The wire is perpendicular to a magnetic field.A force acts on
the wire and the wire moves.
(a) This effect is used in a d.c.motor.
(i) What does the abbreviation d.c.stand for?
(2)Apart from electric motors,name one other device which uses this effect_______________
三：关于左手定律
The first finger points in the direction of the——————which is from ——————to——————
The second finger points in the direction of the--------- which is-from-------- to-----------
The thumb points in the direction of the——————
State two ways in which the force acting on the wire can be increased?
国外物理题（概念）,关于声波的We cannot see a sound wave.However we can see a representation of it by connecting a microphone to————————(b) The pitch of a sound depends on——————————(c) The loudness of
(b) Frequency (c) Amplitude 频率 振幅
（二） （i） direct-current （2） 变压器 Transformer