IB myp 4-5 physics – Practice Questions- All Topics
Topic :Electromagnetism-AC & DC Generation and transmission of electricity
Topic :Electromagnetism– Weightage : 21 %
All Questions for Topic : Electric Fields,Static Electricity ,Magnetism,Magnetic Fields,Current,Power,Voltage,Electric Circuits,Electric and Magnetic Fields,Electromagnetic forces and induction
Question (7 marks)
Question a (1 mark)
Transformers are electrical devices that are used for reducing or increasing the voltage of an alternating current.
Select the correct terms to complete the sentence.
In a transformer that is $100 \%$ efficient, the input ______________ must be ___________________ the output power.
▶️Answer/Explanation
Ans:
In a transformer that is $100 \%$ efficient, the input power must be equal to the output power.
Question b (2 mark)
Transformers are commonly used to reduce the voltage from supply lines to the voltage required for homes.
Use information from the formula sheet to calculate the primary supply voltage. You should assume this transformer is $100 \%$ efficient.
▶️Answer/Explanation
Ans:
Power Primary = Power Seconday
$\mathrm{Vp}~\rm I\mathrm{p}=\mathrm{Vs}~\rm I \mathrm{s}$
$$
\begin{aligned}
& \frac{\rm V p}{\rm V s}=\frac{\rm I s}{\rm I p} \\
& \rm V_ p=\frac{I s \times \rm V s}{\rm I p} \\
& \rm V p=\frac{(240 \times 60)}{1.2}=12000 \\
& \rm V p=12000 \mathrm{~V}
\end{aligned}
$$
Question c (2 mark)
In reality, transformers are only $98 \%$ efficient. Calculate the actual power supplied by the secondary coil.
▶️Answer/Explanation
Ans:
Power Primary $=\rm Vp \rm Ip$
Power Primary $=12000 \times 1.2$
Power Primary $=14400$
transformers are only $98 \%$ efficient, therefore.
actual power supplied by the secondary coil $=0.98 \times 14400$
actual power supplied by the secondary coil is $14112 \mathrm{~W}$