Programme For International Student Assessment Pisa / Sample Science Passage 4: Sunscreens

Mimi and Dean wondered which sunscreen product provides the best protection for their skin. 
Sunscreen products have a Sun Protection Factor (SPF) that shows how well each product absorbs the  ultraviolet radiation component of sunlight. A high SPF sunscreen protects skin for longer than a low SPF sunscreen. 

Mimi thought of a way to compare some different sunscreen products. She and Dean collected the  following: 

- two sheets of clear plastic that do not absorb sunlight; 

- one sheet of light-sensitive paper; 

- mineral oil (M) and a cream containing zinc oxide (ZnO); and 

- four different sunscreens that they called S1, S2, S3, and S4. 

Mimi and Dean included mineral oil because it lets most of the sunlight through, and zinc oxide because  it almost completely blocks sunlight. 

Dean placed a drop of each substance inside a circle marked on one sheet of plastic, then put the second  plastic sheet over the top. He placed a large book on top of both sheets and pressed down. 

 

Mimi then put the plastic sheets on top of the sheet of light-sensitive paper. Light-sensitive paper changes  from dark grey to white (or very light grey), depending on how long it is exposed to sunlight. Finally, 

 

 

Dean placed the sheets in a sunny place. 

 

Plastic sheets 

Light-sensitive paper