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把电流表改装成伏特表,是高中物理的一个重要实验.它的基本原理是在表头上串联一个分压电阻R_(s),R_(s)的大个可由下式决定:R_(s)=V/I_(g)-r_(g)式中r_(g)是表头的内阻.因此在进行表头改装之前必须先测量其内阻.测量表头内阻的方法很多,在高中甲、乙种本中,均用图1所示的电路,用该电路测内阻要求 R≥R＇,r_(g)=R＇才能成立.有些老师反映,条件较差
Changing the ammeter into a voltmeter is an important experiment in high school physics. Its basic principle is to connect a voltage divider resistor R_(s) in series with the header. The large R_(s) can be determined by the following formula: R_(s) =V/I_(g)-r_(g) where r_(g) is the internal resistance of the header. Therefore, the internal resistance must be measured before the header modification. There are many ways to measure the internal resistance of the header. In both A and B versions, the circuit shown in Fig. 1 is used. The internal resistance required by this circuit is R≥R’, r_(g)=R’. Some teachers report that the conditions are poor.