Consider supporting us on Patreon. Help us keep revisedeck free.
21. Alternating currents
A section of Physics, 9702
Listing 10 of 55 questions
Explain what is meant by the root-mean-square (r.m.s.) value of an alternating voltage. An alternating voltage V is represented by the equation V = 220 sin(120πt), where V is measured in volts and t is in seconds. For this alternating voltage, determine the peak voltage, peak voltage = V the r.m.s. voltage, r.m.s. voltage = V the frequency. frequency = Hz The alternating voltage in is applied across a resistor such that the mean power output from the resistor is 1.5 kW. Calculate the resistance of the resistor. resistance = Ω
9702_s10_qp_42
THEORY
2010
Paper 4, Variant 2
View
Explain what is meant by the root-mean-square (r.m.s.) value of an alternating voltage. An alternating voltage V is represented by the equation V = 220 sin(120πt), where V is measured in volts and t is in seconds. For this alternating voltage, determine the peak voltage, peak voltage = V the r.m.s. voltage, r.m.s. voltage = V the frequency. frequency = Hz The alternating voltage in is applied across a resistor such that the mean power output from the resistor is 1.5 kW. Calculate the resistance of the resistor. resistance = Ω
9702_s10_qp_43
THEORY
2010
Paper 4, Variant 3
View
By reference to heating effect, explain what is meant by the root-mean-square (r.m.s.) value of an alternating current. The variations with time t of two currents I1 and I2 are shown in and . –2 –3 –1 t I1 / A –2 –3 –1 t I2 / A Use to determine the peak value and the r.m.s. value of the current I1. peak value = A r.m.s. value = A Use to determine the peak value and the r.m.s. value of the current I2. peak value = A r.m.s. value = A The variation with time t of the supply voltage V to a house is given by the expression V = 240 sin kt where V is in volts, t is in seconds and k is a constant with unit rad s−1. The frequency of the supply voltage is 50 Hz. Determine k to two significant figures. k = rad s−1 The supply voltage is applied to a heater. The mean power of the heater is 3.2 kW. Calculate the resistance of the heater. resistance = Ω
9702_s21_qp_42
THEORY
2021
Paper 4, Variant 2
View
A simple iron-cored transformer is illustrated in . output input primary coil secondary coil iron core State why the primary and secondary coils are wound on a core made of iron. Suggest why thermal energy is generated in the core when the transformer is in use. The root-mean-square (r.m.s.) voltage and current in the primary coil are VP and IP respectively. The r.m.s. voltage and current in the secondary coil are VS and IS respectively. Explain, by reference to direct current, what is meant by the root-mean-square value of an alternating current. Show that, for an ideal transformer, VS VP = IP IS .
9702_w10_qp_41
THEORY
2010
Paper 4, Variant 1
View
A simple iron-cored transformer is illustrated in . output input primary coil secondary coil iron core State why the primary and secondary coils are wound on a core made of iron. Suggest why thermal energy is generated in the core when the transformer is in use. The root-mean-square (r.m.s.) voltage and current in the primary coil are VP and IP respectively. The r.m.s. voltage and current in the secondary coil are VS and IS respectively. Explain, by reference to direct current, what is meant by the root-mean-square value of an alternating current. Show that, for an ideal transformer, VS VP = IP IS .
9702_w10_qp_42
THEORY
2010
Paper 4, Variant 2
View
The mean value of an alternating current is zero. Explain why an alternating current gives rise to a heating effect in a resistor, by reference to heating effect, what is meant by the root-mean-square (r.m.s.) value of an alternating current. A simple iron-cored transformer is illustrated in . primary coil secondary coil iron core State Faraday’s law of electromagnetic induction. Use Faraday’s law to explain why the current in the primary coil is not in phase with the e.m.f. induced in the secondary coil.
9702_w14_qp_41
THEORY
2014
Paper 4, Variant 1
View
Questions Discovered
55