A-LevelPhysicsAlternating currents9702/42 · May/June 2021 · Q108 Marks
By reference to heating effect, explain what is meant by the root-mean-square (r.m.s.) value of an alternating current.
- (a)By reference to heating effect, explain what is meant by the root-mean-square (r.m.s.) value of an alternating current.[2]
- (b)(i)Use [Figure 10.1] to determine the peak value and the r.m.s. value of the current I₁.[1]
- (b)(ii)Use [Figure 10.2] to determine the peak value and the r.m.s. value of the current I₂.[1]
- (c)(i)The frequency of the supply voltage is 50 Hz. Determine k to two significant figures.[2]
- (c)(ii)The supply voltage is applied to a heater. The mean power of the heater is 3.2 kW. Calculate the resistance of the heater.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- [1] the steady current OR the direct current
- [1] that produces the same heating effect (as the alternating current)
- [1] peak current = 2.6 A and r.m.s. current = 1.8 A
- [1] peak current = 2.0 A and r.m.s. current = 2.0 A
- [1] k = 2πf
- [1] = 310 rad s⁻¹
- [1] power = V_RMS² / R_or power = V₀² / 2R
- [1] R = 9.0 Ω
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